Congenitally T and B cell-deficient SCID mice and T cell-deficient NUDE mice, with BALB/c mice as immunologically normal controls, were inoculated with Rhinosporidium seeberi. At 3 and 16 weeks after inoculation, no evidence of rhinosporidiosis was detected. The reasons for the failure to establish rhinosporidiosis in immunodeficient or normal mice remain obscure.