Marked effects on C reactive protein, circulating immune complexes, rheumatoid factor and immunoglobulin levels were demonstrated in a group of 40 patients with rheumatoid arthritis, who received pulse methylprednisolone therapy, either as sole treatment or in combination with a disease modifying agent. The only patient groups in which these serological changes were maintained were the groups taking disease modifying agents, with the more significant and sustained changes occurring in the group of patients who started a disease modifying agent at the time pulse therapy was begun. No significant effect of pulse therapy on neutrophil or lymphocyte counts or lymphocyte subsets could be demonstrated. Pulse therapy, per se, did not have a significant effect on the results of intradermal delayed hypersensitivity testing in any patient group.