The efficacy of Cymelarsan, administered by intramuscular (i/m) injection in the treatment of chronic cases of camel trypanosomosis due to Trypanosoma evansi, was tested under controlled laboratory conditions. It was confirmed that Cymelarsan is a safe drug for use in dromedary camels when administered i/m at dose rates of 0.25 or 0.50 mg/kg body weight. During the 90 days post-treatment no relapses occurred at either dose rate. Hence, the drug was found to be fully effective against the chronic form of the natural disease. A dose of 0.25 mg/kg body weight of Cymelarsan given i/m is recommended.