Expression of the hormone-regulated genes, pS2, prolactin-inducible protein (PIP) and fatty acid synthetase (FAS), was investigated by Northern blotting in primary breast carcinoma, metastatic breast cancer in axillary lymph nodes, in uninvolved breast tissue from mastectomies and in normal lymph nodes. There were considerable differences in expression of the genes between the tissues. The proportion of tissues containing PIP-mRNA decreased from uninvolved breast tissue to primary breast carcinoma to metastatic carcinoma. The reverse applied to FAS-mRNA which was found more often in metastatic cancer than in primary cancer, and least frequently in uninvolved breast tissue. Yet another pattern was observed for pS2 expression. The highest proportion of tissues demonstrating gene expression was found in primary breast cancer with both metastatic tumor and uninvolved breast tissue expressing the gene less frequently. pS2-mRNA and PIP-mRNA could only rarely be detected in trace amounts in normal lymph nodes. In contrast, FAS-mRNA was present in about one third of normal lymph nodes. Only pS2-mRNA showed an association with estrogen and progesterone receptor status.