Human immunodeficiency virus (HIV) was detected in bedbugs (Cimex hemipterus) up to 8 d after oral exposure to highly concentrated virus in blood meals, but no virus replication was observed. HIV did not replicate in either intraabdominally inoculated bedbugs or intrathoracically inoculated mosquitoes (Toxorhynchites amboinensis). The virus was not detected in bedbug feces. Mechanical transmission of HIV by bedbugs could not be demonstrated in an in vitro model. The persistence of HIV in an insect or on its mouthparts is one of many factors necessary for mechanical transmission in nature. The risk of insect transmission of HIV appears to be extremely low or nonexistent.