The principal objectives of this proposal are to measure the serologic prevalence of toxocara canis infection in persons in the United States, to determine the epidemiologic pattern of infection with respect to demographic and geographic factors, and to assess the possible association of infection with visual deficits and ocular disease. For this purpose, we will perform the enzyme-linked immunosorbent assay (ELISA) on 8594 sera which were collected during the National Health and Nutrition Examination Survey of 1971-1973. Detailed demographic, medical, and ophthalmologic information is available for each of the participants. Another objective is to define the clinical, pathological, and immunological response of nonhuman primates with experimental ocular toxocariasis. Cynomolgus monkeys will be infected by either the gastrointestinal or intravitreal route to study the pathogenesis and pattern of larva-specific antibody production in the serum, aqueous and vitreous humor. This information will aid in the interpretation of serologic test results from children with suspected toxocaral visceral larva migrans or ocular toxocariasis.