The effect of ethanol on cell proliferation was studied in Balb/c 3T3 cells and in stably transfected 3T3 cells constitutively overexpressing the human insulin-like growth factor 1 (IGF-1) receptor (p6 cells). Ethanol inhibited growth of both cell lines when they were cultured in serum-free medium supplemented with individual growth factors, i.e. platelet-derived growth factor and IGF-1 for 3T3 cells, and IGF-1 only for p6 cells. Increases in cell number were prevented in both cell lines even when ethanol was present exclusively during the period of IGF-1 stimulation. The inhibitory effect of ethanol was concentration-dependent, with a 30% inhibition observed at 10 mM ethanol. IGF-1 receptor tyrosine autophosphorylation was completely prevented by ethanol both in intact cells and in immunopurified IGF-1 receptor preparations. The binding of IGF-1 to its receptor on intact cells was unaffected by ethanol. Ethanol also inhibited the stimulation of IGF-1 receptor autophosphorylation and the corresponding growth of p6 cells induced by IGF-2. Transcription of c-myc, c-fos, and c-jun in response to IGF-1 was inhibited by ethanol. These findings demonstrate that ethanol at low concentrations markedly inhibits IGF-1 receptor autophosphorylation and IGF-1-mediated cell growth.