We tested sera from 94 patients with systemic lupus erythematosus (SLE) by Western immunoblot. Using the criteria established by the Public Health Service Working Group, 11 (12%) sera were reactive, 29 (31%) indeterminate and 54 (57%) unreactive. When the reactive sera were immunoblotted against an extract from an uninfected control lymphoblastoid cell line, identical bands were obtained. HTLVI antigenemia could not be detected in any of the reactive sera. This suggests that previously described "antibodies to HTLVI" in SLE represent artifactual reaction with cellular components in the antigenic extract.