Spontaneously hypertensive rats (SH rats) were administered drinking water containing 0, 200 or 1000 ppm ascorbic acid with or without 0.5% NaCl and the usual laboratory stock diet for 130 days. The rats given ascorbic acid with or without 0.5% NaCl had a lower mean systolic blood pressure level than that of the respective control group. The difference in the mean blood pressure level from that of the control group was 18-19 mmHg for 200 ppm ascorbic acid group and 30-40 mmHg for 1000 ppm ascorbic acid group. The SH rats were shown to have some defects of ascorbic acid metabolism by lower tissue ascorbic acid levels in the liver, lung and adrenals, and by lower response of ascorbic acid synthesis to a xenobiotic than the Wistar Kyoto rats, which served as the normotensive control rats for SH rats. The abnormalities of ascorbic acid metabolism in the SH rats may be associated with, in part, their high blood pressure, because exogenous ascorbic acid prevented the blood pressure elevation of SH rats, but some other mechanism may also be involved in the effect of ascorbic acid on blood pressure.