Four splenectomized dogs were experimentally infected with Ehrlichia canis and treated at the point of illness with long acting (LA) Oxytetracycline at different dosages. Terramycin LA, when given at a dose of 20 mg/kg body weight (deep intramuscularly) twice, at a four-day interval, was found to have effectively controlled the disease and has replaced the usual 7-14 successive days' treatment regimen when other groups of tetracycline drugs are used. Predef 2X at the rate of 2 mg given intramuscularly concurrently eliminated the local inflammatory reaction caused by the injection of Terramycin LA. Twenty-four out of the 26 naturally infected dogs which were treated in a similar way were completely cured; one died before it could receive the full treatment, and another received a second medication five weeks after the first treatment, showing recurrent epistaxis; blood samples taken from this dog were negative for E. canis.