The effect of five statins, i.e. atorvastatin, fluvastatin, lovastatin, pravastatin and simvastatin was investigated on the proliferation of the human breast cancer cell line MCF-7. All statins except of pravastatin were able to inhibit cell proliferation up to 90 % at a concentration of 50 micro M. Between the effective statins no significant difference was observed indicating a class-specific effect. These data suggest that statins may have clinical significance in the primary prevention of human breast cancer beyond their cholesterol-lowering effect. However, clinical proof must be awaited before drawing any further conclusions.