Because of the known capacity of angiotensin II to serve as a growth factor in multiple tissues, we elected to study the effects of renin-angiotensin system inhibition on the growth of human SH-SY5Y neuroblastoma cells. Cells were treated with captopril (0.05-5 mg/ml), enalapril, or enalaprilat (0.02-5 mg/ml) or saralasin (0.1-0.25 mg/ml). In all cases, statistically significant reductions in cell growth were seen over 5 days of culture. In additional experiments, captopril and enalaprilat significantly decreased thymidine incorporation into DNA in these cells. The administration of angiotensin II in the presence of captopril partially offset these suppressive effects.