Erythrocyte morphologic characteristics and serum chemistry results were studied in 10 gravid ewes during experimental ovine pregnancy-induced hypertension and subsequent administration of the thromboxane synthetase inhibitors CGS13080 and CGS12970. During the hypertensive period mean arterial blood pressure, plasma thromboxane B2 levels, and serum chemistry results, and electrolyte levels were significantly altered. Parameters returned to baseline values or were improved after drug administration. Erythrocyte morphologic features did not change significantly with the onset of the syndrome. Echinocytosis was present during baseline measurement and persisted throughout hypertension. However, after thromboxane synthetase inhibition, percentages of discocytes increased (p less than or equal to 0.005) with the same frequency that echinocyte numbers decreased (p less than or equal to 0.05). Schistocytes were present throughout the study, and changes in their numbers were not detected. Serum phosphorus, blood urea nitrogen, and bilirubin levels and anion gap rose significantly during hypertension and returned to normal levels after drug treatment. We speculate that CGS13080 or CGS12970, by decreasing thromboxane levels and blood pressure, promoted the normalization of erythrocyte membranes.