Eight rabbits, fed on a 1% cholesterol diet for 30 days, were injected daily with potassium chromate for a further 60 days. A 50% reduction in aortic intimal plaque area and in aortic total cholesterol content was observed. However, although levels of serum cholesterol and triglycerides were consistently lower and levels of high density lipoprotein fractions consistently higher in the chromium-treated as compared to the control rabbits, these differences did not reach statistical significance. A further 6 rabbits were injected with potassium chromate and fed on a 1% cholesterol diet for 12 weeks. Mean aortic cholesterol content (+/-SEM) was 40.23 mg/10 cm aortic length (+/-7.50) as compared to 66.24 mg/10 cm (+/- 7.89) in a control group (P less than 0.05), whereas the area of aortic intima covered by macroscopic plaques was 67.5% (+/-2.79) and 81.1% (+/-3.14) (P less than 0.01) respectively.