Daily iv doses of 3 g/kg dimethyl sulfoxide in a 40% solution were given to rhesus monkeys for 9 consecutive days. The monkeys were monitored before and after treatment for 4 mo for changes in blood chemistry, hematology, urine, and ocular, neurological, and cardiovascular systems. At the end of the study all animals were sacrificed and gross and microscopic pathological examinations were performed. No significant or long‐lasting changes were recorded in any of the parameters studied when these data were compared to those for saline controls.