SummaryThe peripheral blood mononuclear cell (PBMN) proliferative responses of cells from patients with schistosomiasis were studied in the presence and absence of indomethacin in the culture medium. PBMN cultures were exposed to antigenic extracts of either adult S. mansoni worms (SWAP) or cercariae (CAP), and assayed for the incorporation of tritiated thymidine. More than 70% of the 48 patients studied with SWAP and the 40 patients studied with CAP, were not substantially effected by the addition of indomethacin to the cultures. The remainder (less than 30%) was augmented more than 50% by indomethacin and comprise a group which gave initially low responses to these antigenic preparations. Further analysis indicated that in some schistosomal patients the effect of an adherent suppressor cell population may, in part, be based on a prostaglandin‐mediated, indomethacin‐sensitive suppressive mechanism. However, the majority of patients, most of whom display adherent suppressor cells, are unaffected by indomethacin. Apparently, other adherent cell suppressor mechanisms are responsible for the regulation obser