Thirty-one of 40 cotton rats (Sigmodon hispidus) collected from central Oklahoma were infected with Strongyloides sp. (78% prevalence). Larvae of Strongyloides sp. (rhabditiform or filariform) were not demonstrable in intestinal contents and scrapings. Female nematodes recovered from intestinal contents and scrapings had morphological similarities with Strongyloides sigmodontis. Cotton rats infected with Strongyloides sp. were indistinguishable clinically from non-infected hosts. Infected animals had no significant gross lesions, but the presence of Strongyloides sp. in the intestinal mucosa was associated with villus atrophy and mild to moderate infiltration of the lamina propria by lymphocytes, plasma cells and occasional eosinophils. Other organs or tissues examined were free from lesions induced by Strongyloides sp.