Three groups of black subjects (systemic lupus erythematosus patients, patients with nonrheumatic disease, and normal subjects) were screened for the expression of the T4 epitope, as recognized by the monoclonal antibody OKT4. We found that the T cell subsets within each group were similar, regardless of the T4 epitope phenotype (intact, intermediate, or deficient). In the subgroup of Jamaican subjects, there was an association between systemic lupus erythematosus and the T4 epitope-intermediate and T4 epitope-deficient phenotypes; this association was not detected in the non-Jamaican population.