Immune responses to individual simian rotavirus (SA 11) structural polypeptides were studied with emphasis on specific IgG, IgM, and IgA in paired sera from four children with rotavirus infections. Responses to simian rotavirus (SA 11) were also studied in 103 healthy children, 10 patients with primary immunodeficiency who received intravenous immunoglobulin, and 11 human immunodeficiency virus antibody-positive patients. All samples were immunoblotted for two major polypeptides--VP2 and VP6--of IgG. Immunoblotted IgA and IgM were elevated 2-4 weeks after the onset of the disease (stage II) in patients with rotavirus infection. Immunoblotted IgG remained almost the same at the onset of the disease and stage II. The scores for primary and secondary immunodeficiency patients were lower than for healthy children. The score obtained by totaling all polypeptides found in each individual was compared with the optical density (OD) value obtained by enzyme immunoassay.