The SV40 transformed murine macrophage cell line, BAC1, proliferates in response to the colony stimulating factor, CSF-1 (Schwarzbaum et al., J. Immunol., 132:1158, 1984). In order to obtain a cell line suitable for biochemical and genetic studies of CSF-1 signal transduction, clones of BAC1 were established. Clones ranged from being completely autonomous to being completely dependent on CSF-1 for growth. Cells of one clone (2F5), which proliferated in response to either CSF-1 or granulocyte-macrophage CSF (GM-CSF) were characterized in detail. The kinetics of receptor-mediated internalization and intracellular destruction of CSF-1 were comparable to the kinetics observed with peritoneal exudate macrophages. CSF-1 was shown to regulate cell spreading, cell survival, protein degradation, and the duration of the G1 and S phases of the cell cycle. The 2F5 clone therefore exhibits a number of CSF-1 stimulated responses and is being used for genetic and biochemical studies of CSF-1 action.