Standard proliferation assays using autoantigens such as S-Ag have given erratic responses when studied with human peripheral blood mononuclear cells. This erratic response is a reflection of the low number of circulating cells in the peripheral blood capable of generating a response as well as the presence of competing cells for the available cytokines in culture. The present study compares the standard proliferation assay with a novel technique in which multiple short-term cell lines are established to S-Ag in medium enriched in helper cytokines. After 12-14 days of culture, these lines were tested for their response to S-Ag. A significant difference was found between patients and controls in the ability to generate responsive cell lines. This translated to a frequency of responsive cells of 0-4 per 10 7 peripheral blood mononuclear cells (PBMC) in normal individuals and 0-200 per 10 7 PBMC in patients. This novel technique may provide a means of determining the number of responsive cells to specific autoantigens in the peripheral blood of patients and the ability to follow the response over time.