Baboons (Papio anubis) were injected in the leg muscle with 18,000 20 Krad irradiated schistosomula of Schistosoma haematobium. Four protocols were followed: single, primary injection; single injection into animals primed by patent S. haematobium infection; secondary vaccine injection following an earlier injection; and single injection following praziquantel treatment of infected animals. Injection of the putative vaccine elicited localized mixed inflammatory infiltration at the site of injection which was both intense and prolonged. Three grades of tissue reaction were seen: the relatively mild primary response; the response in infected animals which had enhanced tissue eosinophilia; and the response in animals primed by prior injection and drug-treated prior infection. The latter 2 showed intensification of eosinophilia, stellate abscesses in the lesion centers, and perischistosomular Hoeppli precipitates. Intramuscular lesions peaked at 14 days for the primary response and at 7 days for all secondary responses. Traces of the milder lesions persisted beyond 4 weeks; more severe reactions healed more rapidly. Some schistosomula survived for 14 days in the milder reactions. A few larvae were deposited in the skin by backflushing of the injectate which produced local inflammation. Compared to mice, live schistosome vaccines injected into baboons elicited greater local inflammation; however, while evidence suggested that sporadic vaccine schistosomula did reach the lymphatic nodes draining the injection sites, no systemic lesions were found and the injection sites healed in ∼5–6 weeks without permanent damage.