The relative expression in human breast cancer cells of messenger ribonucleic acids (mRNA) encoding different steroid hormone receptors is unknown. Accordingly, mRNA levels in total RNA extracted from 13 human breast cancer cell lines were measured by Northern analysis employing complementary DNA probes for the human oestrogen (ER), progesterone (PR), androgen (AR), vitamin D3 (VDR) and glucocorticoid receptors (GR). The 7 ER+ lines expressed a single 6.4 kilobases (kb) ER mRNA. Interestingly, low concentrations of ER mRNA were detected in the ER- cell lines, MDA-MB-330 and BT 20. PR mRNA, predominantly a 13.5 kb species, was expressed in the 6 lines known to be ER+, PR+ by radioligand binding; however, one ER+ cell line, MDA-MB-134, failed to express PR mRNA. A 10.5 kb AR mRNA was expressed at significantly higher levels in ER+ than ER- cell lines. All cell lines expressed a single 4.6 kb mRNA for VDR and a single 7.4 kb mRNA for GR. ER and PR mRNA levels were positively correlated (p = 0.011) and each was positively correlated with androgen receptor (AR) mRNA levels (p less than or equal to 0.009). ER, PR and AR mRNAs were negatively associated with GR levels (p less than or equal to 0.012), while ER and AR mRNA levels were negatively correlated with mRNA for the epidermal growth factor receptor. In contrast, levels of VDR mRNA were unrelated to the concentration of any other steroid receptor mRNA. Our data demonstrate the coordinate expression of ER, PR and AR genes, and an inverse relationship between sex steroid hormone receptor and GR gene expression in human breast cancer cell lines.