Healthy camels were experimentally infected with Trypanosoma evansi and then treated with isometamidium chloride (samorin) at single intravenous doses of 0.5 or 1.0 mg/kg. Five to 10 min after the drug administration, the camels at both dosages showed lacrimation, salivation, trembling, restlessness, frequent urination and defecation, followed by diarrhea. Moreover, the camels at the higher dose showed an unsteady gait for about an hour with hindleg weakness and walking backward. The animals fell to the ground, laid on their sides, and bent their necks into an "S" shaped curve. Three hours after the drug administration all the animals stood up and remained quiet. The treatment increased the concentration of plasma ammonia and total protein. No significant change was found in the plasma bilirubin concentration. Two hours after treatment, the activity of plasma cholinesterase was significantly reduced. The enzyme activity recovered 24 h after drug administration, but was still significantly below the control value. The treatment did not produce statistically significant changes in the hemogram of the infected camels. The results suggest that the drug should not be used clinically against T evansi infection due to its low margin of safety. If the drug is to be used at all in camels, pretreatment with an anticholinergic agent might be considered.