A series of acyl derivatives e.g., I [R = Me, Et, CO2H (CH2)nCO2H, CH:CHCO2R1, CH2NH2, CH2NMe2, (CH2)2NH2; n = 1-3; R1 = H, Et] of 2-(m-hydroxyphenyl)imidazo[2,1-b]benzothiazole (II), a selective immunosuppressive agent for delayed type hypersensitivity (DTH), was prepared and tested for its suppressive activity of DTH in mice after oral administration.Six compounds were more potent immunosuppressive agents than II but they showed no effect on humoral immunity as in the case of II.