Female rats were exposed to a drinking solution containing 157 parts per million (ppm) of the organophosphate insecticide diazinon for 14 days. Plasma samples were assayed for prothrombin time (PT), partial thromboplastin time (APTT), hematocrit (HCT), platelet count (PLT) and clotting times for coagulation factors I (Fibrinogen), II, V, VII, VIII, X and XII. Significant change following ingestion of diazinon were noted for the PT, APTT, Fibrinogen, factors II, VII, VIII, X, XII and hematocrit. The data suggest that in the rat, diazinon ingestion has a direct effect on the clotting activity of various blood coagulation parameters.