The usefulness of a human enzyme-linked immunosorbent assay (ELISA) for Baylisascaris procyonis larval migrans was assessed in non-human primates (NHP). The test is a research assay performed at Purdue University. Six cooperating zoos submitted 259 NHP serum samples, spanning these major phylogenetic groups: I) prosimians (n=54); II) New World monkeys (20); III) Old World monkeys (84); and IV) hominoids (101). Sera were tested in duplicate using a microtiter-well ELISA using B. procyonis larval excretory-secretory proteins as antigen, and serum from an experimentally infected baboon as positive control (courtesy of Centers for Disease Control). The ELISA clearly identified seropositive animals in all zoos. Using putative cutoffs of optical density (OD405) <0.150=negative; indeterminate; and >0.250=positive, 150 (57.9%) were clearly negative (mean OD 0.046) and 76 (29.3%) clearly positive (mean OD 0.657, range 0.253–1.773). Of these, 15 were high positive, with OD 1.095–1.773 (mean, 1.314); another 21 ranged from 0.530–0.998. Positive animals were seen from all zoos, and 74 (95%) were great 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 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.