Dissemination of fungal infection due to Coccidioides immitis has been previously shown to be related to hereditary factors. Two associations reported to date are race (e.g., Filipino and black ancestry) and HLA histocompatibility type (HLA-19). In the present study of 105 patients a significant association of blood group B and dissemination is demonstrated. C. immitis is known to possess antigens with blood group A activity. Previous epidemiologic studies have also shown HLA-A9 and blood group B are both more common in persons of black and Filipino ancestry. Further studies are needed to define whether these are independent variables, and may define subgroups at particularly high risk following coccidioidal infection.