diff --git a/frontend/biochem-library.html b/frontend/biochem-library.html
index de09ac6..1fb1ddf 100644
--- a/frontend/biochem-library.html
+++ b/frontend/biochem-library.html
@@ -612,5 +612,6 @@ init();
 </script>
 <script src="/js/notifications.js"></script>
 <script src="/js/mobile.js"></script>
+<script src="/js/biochem-nav.js"></script>
 </body>
 </html>
diff --git a/frontend/biochem-pathways.html b/frontend/biochem-pathways.html
index 7e20a35..e7c0ae3 100644
--- a/frontend/biochem-pathways.html
+++ b/frontend/biochem-pathways.html
@@ -1040,5 +1040,6 @@ init();
 </script>
 <script src="/js/notifications.js"></script>
 <script src="/js/mobile.js"></script>
+<script src="/js/biochem-nav.js"></script>
 </body>
 </html>
diff --git a/frontend/biochem-properties.html b/frontend/biochem-properties.html
index 6dc28e1..c928f5a 100644
--- a/frontend/biochem-properties.html
+++ b/frontend/biochem-properties.html
@@ -618,5 +618,6 @@ LS.hideDisabledFeatures?.();
 </script>
 <script src="/js/notifications.js"></script>
 <script src="/js/mobile.js"></script>
+<script src="/js/biochem-nav.js"></script>
 </body>
 </html>
diff --git a/frontend/biochem-reactions.html b/frontend/biochem-reactions.html
index a57123d..796c3e4 100644
--- a/frontend/biochem-reactions.html
+++ b/frontend/biochem-reactions.html
@@ -836,5 +836,6 @@ init();
 </script>
 <script src="/js/notifications.js"></script>
 <script src="/js/mobile.js"></script>
+<script src="/js/biochem-nav.js"></script>
 </body>
 </html>
diff --git a/frontend/biochem.html b/frontend/biochem.html
index 19ee569..469bdbc 100644
--- a/frontend/biochem.html
+++ b/frontend/biochem.html
@@ -2001,5 +2001,6 @@ LS.loadFeatures?.().then(feats => {
 <script src="/js/notifications.js"></script>
 <script src="/js/search.js"></script>
 <script src="/js/mobile.js"></script>
+<script src="/js/biochem-nav.js"></script>
 </body>
 </html>
diff --git a/frontend/js/biochem-nav.js b/frontend/js/biochem-nav.js
new file mode 100644
index 0000000..bb73aaa
--- /dev/null
+++ b/frontend/js/biochem-nav.js
@@ -0,0 +1,81 @@
+'use strict';
+/*
+ * biochem-nav.js — межстраничная навигация модуля «Биохимия».
+ * Подключается на всех 5 страницах; вставляет полосу после шапки.
+ * Текущая страница определяется по location.pathname.
+ */
+(function () {
+  const PAGES = [
+    { path: '/biochem',            icon: 'M9 3h6M10 3v6l-5.4 9.3A1.5 1.5 0 0 0 5.9 21h12.2a1.5 1.5 0 0 0 1.3-2.3L14 9V3M7.5 15h9', label: 'Редактор' },
+    { path: '/biochem-library',    icon: 'M4 5a2 2 0 0 1 2-2h6v17H6a2 2 0 0 0-2 2z M20 5a2 2 0 0 0-2-2h-6v17h6a2 2 0 0 1 2 2z', label: 'Библиотека' },
+    { path: '/biochem-reactions',  icon: 'M13 2 3 14h9l-1 8 10-12h-9l1-8z', label: 'Реакции' },
+    { path: '/biochem-properties', icon: 'M9 17H7A5 5 0 0 1 7 7h2 M15 7h2a5 5 0 0 1 0 10h-2 M9 12h6', label: 'Свойства' },
+    { path: '/biochem-pathways',   icon: 'M6 18h8 M3 22h18 M8 22V12l4-10 4 10v10 M10 9h4', label: 'Пути' },
+  ];
+
+  function current() {
+    const p = location.pathname.replace(/\.html$/, '');
+    return PAGES.find(pg => p === pg.path || p.endsWith(pg.path)) || null;
+  }
+
+  function render() {
+    const cur = current();
+    const nav = document.createElement('nav');
+    nav.className = 'biochem-subnav';
+    nav.setAttribute('aria-label', 'Разделы биохимии');
+    nav.innerHTML = PAGES.map(pg => {
+      const active = cur && cur.path === pg.path;
+      const href = pg.path + (pg.path === '/biochem' ? '' : '.html');
+      return `<a class="bsn-tab${active ? ' bsn-active' : ''}" href="${href}" aria-current="${active ? 'page' : 'false'}">
+        <svg class="ic xs" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.9" stroke-linecap="round" stroke-linejoin="round"><path d="${pg.icon}"/></svg>
+        <span>${pg.label}</span>
+      </a>`;
+    }).join('');
+
+    // inject CSS once
+    if (!document.getElementById('biochem-subnav-style')) {
+      const s = document.createElement('style');
+      s.id = 'biochem-subnav-style';
+      s.textContent = `
+        .biochem-subnav {
+          display: flex; align-items: center; gap: 2px;
+          padding: 0 20px;
+          background: rgba(255,255,255,0.75); backdrop-filter: blur(8px);
+          border-bottom: 1.5px solid rgba(15,23,42,0.07);
+          flex-shrink: 0; position: sticky; top: 0; z-index: 60;
+        }
+        .bsn-tab {
+          display: inline-flex; align-items: center; gap: 7px;
+          padding: 10px 14px; border-radius: 8px;
+          font-family: 'Manrope', sans-serif; font-size: 0.82rem; font-weight: 600;
+          color: var(--text-3, #56687A); text-decoration: none;
+          transition: background .14s, color .14s; border-bottom: 2px solid transparent;
+          white-space: nowrap;
+        }
+        .bsn-tab .ic { stroke: currentColor; flex-shrink: 0; }
+        .bsn-tab:hover { background: rgba(155,93,229,0.07); color: var(--violet, #9B5DE5); }
+        .bsn-active {
+          color: var(--violet, #9B5DE5); font-weight: 700;
+          border-bottom-color: var(--violet, #9B5DE5);
+        }
+        .bsn-active:hover { background: rgba(155,93,229,0.07); }
+        @media (max-width: 560px) {
+          .biochem-subnav { padding: 0 8px; gap: 0; overflow-x: auto; }
+          .bsn-tab { padding: 9px 10px; font-size: 0.76rem; }
+          .bsn-tab span { display: none; }
+          .bsn-tab .ic { width: 16px; height: 16px; }
+        }
+      `;
+      document.head.appendChild(s);
+    }
+
+    // insert: after sidebar/notif-drop, before first content element inside sb-content
+    const sbContent = document.querySelector('.sb-content');
+    if (sbContent) {
+      sbContent.insertBefore(nav, sbContent.firstChild);
+    }
+  }
+
+  if (document.readyState === 'loading') document.addEventListener('DOMContentLoaded', render);
+  else render();
+})();