The macrophage-specific colony stimulating factor CSF-1 is required for the growth and differentiation of monocytes. The cell surface receptor for CSF-1 is identical to the product of the c-fms proto-oncogene. The present studies have monitored CSF-1 and c-fms expression in human carcinoma cell lines. Two of three human ovarian carcinoma cell-lines expressed multiple species of CSF-1 mRNA. Furthermore, detection of CSF-1 transcripts was associated with secretion of CSF-1 protein that was increased after phorbol ester treatment. CSF-1 mRNA was also detectable in 4 breast and 2 lung carcinoma cell lines. In contrast, c-fms expression was found only in SK-Br-3 breast carcinoma cells. Similar studies in 2 human choriocarcinoma cell lines demonstrated the presence of c-fms, but not CSF-1, transcripts. While phorbol ester treatment was associated with increased c-fms mRNA levels in choriocarcinoma cells, this agent had no effect on CSF-1 expression. These findings indicate that: 1) CSF-1 expression is frequent in human ovarian, breast and lung carcinoma cells; and 2) coexpression of the CSF-1 and c-fms genes, as found in monocytes is infrequent in malignant epithelial and choriocarcinoma cell lines.