In the course of studies on compounds with expected antiinflammatory and immunosuppressive activity a series of new derivatives of tetrahydro [1,3]-thiazine-4-one-6-carboxylic acid, tetrahydro [1,3]-thiazine-4,6-dione and 2-thiobarbituric acid have been synthetized. Several new and unexpected details of the chemical behavior of these compounds were revealed. The chemical structure of the new compounds was confirmed by degradation and identification of the decomposition products and spectral analysis. Pharmacologic analysis showed that some of the compounds exerted an antiinflammatory and immunosuppressive activity.