The effects of CV-2619 on the half-life and hemolysis of red blood cells (RBC) in stroke-prone spontaneously hypertensive rats (SHRSP) were examined. The half-life of RBC in SHRSP was shorter than that in control Wistar Kyoto rats (WKY) and was significantly prolonged in SHRSP kept on a diet containing 0.1% (w/w) of CV-2619 (calculated at 71.0 mg/kg/day): 11.7 +/- 0.4 days in untreated SHRSP (n = 11); 13.8 +/- 0.1 days in treated SHRSP (n = 5, P less than 0.01); and 14.8 +/- 0.5 days in WKY (n = 6). The hemolysis of RBC in salt-loaded SHRSP was accelerated compared with that in WKY. In SHRSP given CV-2619 (20 or 70 mg/kg/day, p.o.) for 2 weeks, the hemolysis was significantly inhibited; the percent hemolysis was 43.9 +/- 0.9% (n = 10) in the control, 39.5 +/- 0.9% (n = 9, P less than 0.01) in the group given 20 mg/kg CV-2619, and 37.1 +/- 0.8% (n = 9, P less than 0.001) in the group given 70 mg/kg CV-2619. These results suggest that the stabilizing effect of CV-2619 on the membrane of RBC is involved in its therapeutic effects in cerebral vascular disorders.