An orally administered hemorheologic drug, propentofyliine, was evaluated for the treatment of navicular disease. In a preclinical trial, 6 normal horses and 3 with navicular disease were administered the drug for 3 consecutive 30-day periods at incremental dose rates of 5, 10 and 15 mg/kg twice daily, respectively. An adverse response to the medication was assessed for by monitoring physical, complete blood count and serum biochemistry parameters, and by completing a necropsy examination. No abnormalities were noted in response to drug administration. A pharmacological effect was sought by monitoring the drug's influence on platelet aggregation percent (PAP) and rate (PAR). A significant (P