Correlation between expression status of bcl-2 products and cell growth fraction (estimated by immunostaining for Ki-67 antigen) was analyzed in human endometrial adenocarcinoma tissue in situ. For this, serial sections, 2 micrometers thick, from formalin-fixed and paraffin-embedded tissue samples of 10 cases of the carcinoma were examined. Nine out of 10 carcinomas contained both bcl-2 positive and negative nests when examined immunohistochemically. In the remaining one case, no positive reaction for bcl-2 was observed. In general, bcl-2 positive nests tended to contain quiescent (Ki-67 negative) carcinoma cells, and bcl-2 negative nests, on the contrary, a large fraction of proliferating (Ki-67 positive) cells. However, this correlation was not strict, and in a few nests, the level of growth fraction was observed to be similar irrespective of bcl-2 positivity. These results show the complex function(s) of bcl-2 products, when considering their apoptosis-suppressing effects, cell cycle dependence and influence on cell proliferation status. Further, the results suggest an altered regulation of oncogene products in human solid tumor tissue in vivo.