TEI-3096 [6-p-chlorobenzyl-5H-2,3,6,7-terahydro-5,7-dioxothiazolo (3,2-a) pyrimidine], a novel thiazolopyrimidine compound has been shown to suppress adjuvant arthritis in rats without any effect on conventional inflammation. We examined the immuno-pharmacological profile of TEI-3096 in murine lymphocytes. The blastformation induced by Con A or LPS was inhibited by addition of 50-500 microM concentrations of TEI-3096. This compound suppressed elevated plaque-forming cell (PFC) response against T cell-dependent antigen. However, TEI-3096 had no effect either on normal PFC response or on antibody formation against T cell independent antigen. Although orally administered TEI-3096 had no obvious effect on anti-SRBC PFC response in normal mice, it normalized the colchicine-induced enhancement of antibody formation against TNP-HGG. TEI-3096 also enhanced the delayed type hypersensitivity in mice and rats. These results suggests that TEI-3096 restores the abnormal immune response. Therefore, it may be useful for the treatment of auto-immune disease such as rheumatoid arthritis.