PCT No. PCT / RU97 / 00098 Sec. 371 Date Mar. 17, 1998 Sec. 102(e) Date Mar. 17, 1998 PCT Filed Apr. 2, 1997 PCT Pub. No. WO98 / 43982 PCT Pub. Date Aug. 10, 1998Biologically active substance on the basis of tetracyclicnitrogen heterocycles of pyrimidine row for treating tuberculosis, mycobacteriousis, viral diseases, infections caused by chlamydias, and also diseases which are accompanied by immunodeficiency, in particular malignant neoplasm, has high antimicrobial activity, in particular to strains of mycobacteria which are resistant to the prototype-isoniazid, and simultaneously possess antiviral activity (relative to herpes simplex viruses), antichylamidial activity and also stimulate production of endogenic interferons in organisms. It represents a derivative of 5-oxo-5H-[1]-benzopyrano-[5,6-b]-4-oxo-4H-[1,2]-pyrimido-1,4,5,6-tetrahydro-1,3-thiazine (1) of general formula(1). (I-X) where: R1-H or halogen; R2-H, or halogen, or nitro-group, or hydroxy-group or methoxy-group.