Rats were kept at −20°C until they died. Stomach erosions were found in every rat exposed to cold. Histamine and serotonin were visualized by fluorescence microscopy and their quantities were measured fluorometrically. Histamine fluorescence had disappeared in the erosion region from mucosal mast cells and enterochromaffin-like cells. Submucosal mast cells had retained full fluorescence and showed no degranulation. The amine content showed an insignificant decrease. Serotonin fluorescence had also disappeared from the mucosal mast cells in the erosion, but was visible in enterochromaffin cells and submucosal mast cells beneath the erosion. Degranulation of mucosal mast cells was confirmed in sections stained by toluidine blue. Gastric serotonin level was significantly lower in the test group than in the control group (0.58±0.23 μ/g versus 0.99±0.28 μ/g). The results confirmed the effectiveness of cold exposure in causing gastric erosion in the rat. Direct evidence of the release of histamine and serotonin from the mucosal cells during formation of erosions was obtained.