Anti-human pepsinogen (PG) I and II monoclonal antibodies were used in an immunohistochemical study of 56 cases of gastric carcinoma (37 early stage and 19 advanced stage). We examined the relationship between positivity of the carcinoma for producing PG I and II and serum PG I and II levels. We found that in 2 cases (3.6%), the carcinoma produced PG I and in 11 cases (19.6%), it produced PG II. Early gastric carcinomas and differentiated-type carcinomas produced PG II more frequently than advanced and undifferentiated-type carcinomas. Also, type II c carcinomas and carcinomas located in the C area of the stomach produced PG II more frequently. But there was no significant difference between PG I and II-positive and negative cases in relation to both serum PG I and II levels. Moreover, the rate of positivity did not correlate with cases of abnormally high levels of serum PG I and II, (except in 1 case with abnormally high serum PG I in which PG II was produced.) These results suggest that there is no significant relationship between PG I or II-producing gastric carcinomas and serum PG levels. Furthermore, we examined PG II-producing and non-producing carcinomas in relation to the grade of inflammation, atrophy and intestinal metaplasia in gastric mucosa. However, there was no statistically significant difference among these factors. Only serum PG I and II levels were related to these parameters.