Nivolumab (10 and 50 mg/kg, i.v.) is well tolerated in cynomolgus monkeys. Serum chemistry changes are limited to a reversible 28% decrease in T3 at week 13 in females treated with 50 mg/kg. T4 and TSH levels are unchanged. In males treated with 50 mg/kg, there are no changes in T3, T4, or TSH levels. Nivolumab exposure increases in an approximately dose-proportional manner between 10 and 50 mg/kg, with no substantial sex differences noted.