Attempts were made to transmit O. volvulus infection to small laboratory animals and several species of primates to identify a practical laboratory host for human onchocerciasis. Infective larvae of O. volvulus of Guatemalan origin were inoculated into the following animals: rhesus monkeys, bonnet monkeys, golden spider monkeys, black spider monkeys, galagos, opossums, jirds, newborn and adult Swiss mice, kinkajou, cebus monkey, normal and splenectomized multimammate rats, and a calf. The animals were examined for signs of developing infection for up to two years after inoculation. None of the animals tested developed a patent infection, and neither larvae nor O. volvulus adults were found during the necropsy of all the animals which died or were killed during or at the end of the examination period. It is concluded that none of the animals tested is susceptible to infection with O. volvulus.