Cellular and humoral immune responses were assessed in 24 patients with systemic sclerosis and matched controls by immunization with a thymus dependent (TD) antigen, keyhole limpet hemocyanin (KLH), a and thymus independent (TI) antigen, dinitrophenylated Ficoll (DNP-Ficoll). Cell mediated immunity in the patients with systemic sclerosis expressed as delayed cutaneous hypersensitivity to KLH, as well as the primary T dependent and T independent antibody responses were normal. Our findings suggest that there is no generalized defect in the immune responsiveness of patients with systemic sclerosis. There is however evidence that specific defects may occur in certain subsets of patients with systemic sclerosis.