['Movement of unfractionated (UFH) and low molecular weight heparins (LMWHs) through gastric mucosa was compared to determine effect of molecular weight on absorption.', "Rat gastric mucosa, mounted in an Ussing chamber, was bathed in oxygenated Kreb's buffer, containing mannitol on the mucosal (lumen) at pH 7.4 or 4, and glucose on the serosal side (circulation) at pH 7.4. Heparins (10 mg/ml) were added to the mucosal side. Potential difference (PD), resistance, and short circuit current (Isc), were determined. Buffers and tissues were extracted to measure heparin by gel electrophoresis.", 'PD increased on heparin addition and following a lag period, that was longer for UFH at pH 7.4 and LMWHs at pH 4.0, returned to baseline. Isc increased slightly for UFH at pH 4.0 but significantly for LMWHs at pH 7.4. More UFH or LMWHs were recovered from serosal buffers at pH 4.0 and pH 7.4 respectively. Results suggest UFH and LMWHs cross gastric mucosa faster, and active transport is involved, at pH 4.0 and pH 7.4, respectively.'] Is movement of heparins across rat gastric mucosa dependent on molecular weight and pH?