No consistent deleterious effects directly attributable to the nuclear polyhedrosis virus,Baculovirus heliothis, were observed when rhesus monkeys,Macaca mulattaL., were exposed to the virus once or weekly for 26 weeks by subcutaneous injection, inhalation, or oral gavage. A greater frequency of lymphoid hyperplasia in lymph nodes was observed in treated monkeys, but infective virus was not found in these nodes. Body-weight gains, temperature, hematology, blood chemistry, and histopathology of treated monkeys were similar to those of untreated monkeys. Infective virus, viral antibodies, or viral antigens were not found in blood drawn from treated monkeys.