The activity of a mixture of sulphadimethoxine and pyrimethamine (10:3) as prophylactic medication and prophylactic and therapeutic medication was studied in rabbits experimentally infected with Eimeria stiedai. The haematocrit index (packed cell volume) and haemoglobin levels were studied for assessment of drug toxicity. The activity in serum of aspartate aminotransferase (AST) and alanine aminotransferase, alkaline phosphatase and gamma-glutamyltranspeptidase were studied as indicators of hepatic lesions. Parasite development was followed on the basis of the presence of oocysts; other parameters were analysed in order to monitor the performance of infected animals. All the parameters studied showed that the chemoprophylactic medication provided efficient control of the infection and of the hepatic lesions. Serum AST activity was seen to be a good indicator of the effect of the drugs on the liver.