The usefulness of a human enzyme-linked immunosorbent assay (ELISA) for serological diagnosis of Baylisascaris procyonis larva migrans was assessed in nonhuman primates (NHP). The test was originally developed as an assay performed on human samples at Purdue University. Six participating zoos submitted 258 NHP serum samples, spanning these major phylogenetic groups: 1) great apes (n = 84), 2) lesser apes (n = 17), 3) Old World monkeys (n = 84), 4) New World monkeys (n = 20), and 5) prosimians (n = 53). Sera were tested in duplicate using a microtiter-well ELISA with B. procyonis larval excretory-secretory proteins as antigen, and serum from an experimentally infected baboon (Papio anubis) served as positive control. The ELISA clearly identified seropositive animals in all zoos. With putative cutoffs of optical density (OD) measured at 405 nm (OD405) of <0.150 = negative, 0.150–0.250 = indeterminate, and >0.250 = positive, 149 of 258 (57.8%) were clearly negative (mean OD 0.046), and 78 of 258 (30.2%) were clearly positive (mean OD 0.657, range 0.253–1.773), the rest being indeterminate. Of these, 15 were high positive with OD 1.095–1.773 (mean 1.314). Positive animals were seen from all zoos; 76 (97.4%) were great apes, lesser apes, or Old World monkeys. The four highest ODs were in a siamang (Symphalangus syndactylus), lion-tailed macaque (Macaca silenus), Sumatran orangutan (Pongo abelii), and western lowland gorilla (Gorilla gorilla gorilla), all from different zoos. Prosimians had a mean OD of 0.039 and New World monkeys 0.021, indicating that human reagents either did not work for these groups or few infected animals were represented. These results indicate that the human ELISA for B. procyonis works well for at least higher phylogeny NHP and that serologic evidence of infection is surprisingly common, correlating with what is known for exposure to this parasite in zoos.