Rel A protein was in complex with IκB in the cytoplasm of patient T cells and was insensitive to stimulation. Cytoplasmic extracts from control and patient T cells were immunoprecipitated with anti-RelA antibody and the immunoprecipitates were subjected to immunoblotting using anti-IκB and anti-RelA antibodies, respectively. In control immunoprecipitations, normal rabbit IgG was added to cytoplasmic extract from a healthy individual. Similar results were obtained with 2 additional patients.