Abstract Several new amides 4 of 5-substituted 3-methyl-4-isothiazolecarboxylic acid were obtained. These compounds have acetylamino or benzoylamino groups in position 5 of the isothiazole ring. In position 4, the carboxylic group was transformed in the amides using amino-acid esters. Activities of the obtained derivatives were checked in the humoral immune response and delayed type hypersensitivity reaction to sheep red blood cells ( ...