We analyzed the proliferative response of DA1, DA1-a, NFS 60, 32DC1, Ea 3-17 and FDCP2 murine interleukin 3 (mIL3)-sensitive cell lines to human recombinant IL1 alpha, IL1 beta, IL2, IL4, IL5, IL6, granulocyte-CSF (G-CSF), macrophage-CSF (M-CSF), granulocyte-macrophage-CSF (GM-CSF), interferon gamma (IFN gamma), tumor necrosis factor (TNF) alpha, gibbon IL3, purified HILDA and mouse recombinant IL3, IL4, GM-CSF. All cell lines responded to mIL3 and IL4. Various response patterns were observed with human IL2, G-CSF and murine GM-CSF. Human IL4 and GM-CSF were absolutely inefficient in triggering proliferation of lines sensitive to their murine counterparts, confirming the species specificity of these two cytokines. Among the cell lines responding to G-CSF, some variations in sensitivities were observed. Thus the 32DC1 cell line needed 10 to 30 times more G-CSF to reach the same level of proliferation as the NFS60 cell line. DA1-a was the only factor-dependent cell line responding to purified HILDA, and IL6 was found to trigger proliferation of the NFS60 cell line, with a half-maximum effect observed for 0.1 pM of hormone.