PURPOSE: Recent studies have shown that the expression of mucin is organ- and cell-type specific and it is increasingly possible that its change could result from oncogene activation.To evaluate histogenesis and prognostic factors for gastric carcinoma, we studied the oncoprotein expression in gastric cancer cells classified by mucin phenotye. MATERIALS AND METHODS: Mucin histochemistry and immunohistochemistry for ras, c-erbB2, and p53 oncoprotein expression were performed in 101 surgically resected gastric carcinoma specimens. PAS-Con A, GOS, and HID-AB staining techniques were employed in identifying mucosubstances, RESULTS: Of the 101 specimens studied, 73(72.3%) revealed as having mixture of various mucin-secreting cancer cells. Overall, ras immunoreactivity was observed in 72(71.3%), c-erbB2 in 7(6.9%), and p53 in 47(46.5%). Of the 73 mucus-secreting carcinomas, the surface mucous cell type were shown in 65 (89.0%), the pyloric gland cell type in 48(65,8%), the sialomucin type in 47(64.4%), and the sulfomucin type in 54(74.0%). There was significant association between mucin secretion and ras expression, but not c-erbB2 and p53 expression. There was no significant association between mucin secreting cell types and Lauren classification. Ras expression was correlated with serosal invasion, lymph node metastasis and poor prognosis. CONCLUSION: The phenotypic expression by mucin histochemistry may be not more important for studying of histogenesis in gastric carcinoma than Lauren classification. Ras expression is a poor prognostic indicator and may be correlated with phenotypic expression of surface mucous cell and intestinal cell type in gastric carcinoma.