Interferons (IFNs) have an anti-proliferative effect on various cell lines. The molecular basis for these effects has not yet been determined but it is presumed that most, if not all, the biological effects of IFNs are mediated by a set of IFN-inducible genes and their protein products. Our earlier study using MCF-7 cells (Tiwari RK et al: Br Cancer Res Treat 18: 33-41, 1991) showed that IFNs were anti-proliferative and the kinetics of induction of the IFN-inducible genes correlated well with the time of maximal cytostatic effect. In the present communication, we have characterized the effect of type I and II interferons on an estrogen receptor negative cell line, BT-20. IFNs were found to be anti-proliferative in these cells and a number of the IFN-inducible genes were also induced. While we observed a number of similarities in the kinetics of induction of these genes in BT-20 and MCF-7 cells, we also observed some notable differences. mRNA 561, which was inducible by both types of interferons in MCF-7 cells, was not induced by IFN-gamma in BT-20 cells. mRNA 6-16 was induced in both cells by both IFNs, however, we observed differences in the manner the matured RNA is spliced. mRNA of two sizes (1.4 and 1.0 kb) were observed in BT-20 cells and only one (1.0 kb) in MCF-7 cells. Our results conclude that the biological effect of IFNs depends largely on specific cell characteristics and the presence or absence of estrogen receptors may affect the expression of IFN-responsive mRNAs.