Two litters of eight-week-old, IgA-deficient pups, each including one normal littermate control, were infected with 5,000 infective third-stage Strongyloides stercoralis larvae per pup. No significant differences between the dogs deficient in serum and mucosal IgA and the normal control dogs were observed in any of the parasitologic parameters measured during the course of infection. The time required to reach patency, the maximum number of larvae shed in the feces, the number of days postinfection at which larval shedding was at its maximum, and the time required to eliminate shedding were similar in the two groups. Once larval shedding ceased, there was no recrudescence, even though serum and fecal IgA were absent or low throughout the seven-month course of the investigation. All dogs remained asymptomatic, with complete blood counts and clinical chemistries within normal ranges. In addition, serum IgM and IgG levels were within the normal range for both groups of infected dogs. All dogs from which necropsy samples were obtained harbored low numbers of adult female worms, some of which were barren. An IgA deficiency apparently does not affect the course or severity of S. stercoralis infection in the dog.