In part I and II, the antibacterial or bactricidal action of photosensensitizing dyes was reported. In the present part, the author studied the influence of 14 sorts of photsensitizing dyes on the bacterial metabolism and respiration by means of warburg apparatus. Salmonella typhi 57S and Staphylococus aureus (Terashima) were used as the test organisms, and 10(-2)M glucose as the substrate. The photosensitizing dyes of several concentrations around their antibacterial concentrations were used ror experiments. The results are briefly summarized as follows; 1. As for the inhibitory action of monomethin cyanine group dyes to the respiration of Sal. typhi, NK 564 (3, 3'-di-n-hepthyl-4, 4'-dimethyl-2, 2'-monomethine th azolocyanine-3-chloride) was the strongest, and it decreased in the order of NK 570 (3, 3'-di-n-octhl-4, 4'dimethyl-2, 2'-monomethine thiazolocyanine-3 acetate), NK 266 (3, 3'-di-n-hepthyl-4, 4'-dimetyl-2, 2'-monomethine thiazolocyanine-3-iodide) and NK 400 (3, 3'-n-octhyl-4'-dimethyl-2, 2'-monomethine thiazolo cyanine-3-iodide): this fact suggests that the inhibition of the respiration of Sal. typhi depends upon the number of carbon of alkyl radical and C(7)H(15) is stronger than C(8)H(17). To the repiration of Staph. auueus, NK 564 showed the strongest inhibition, and this inhibition decreased in the order of NK 570, NK 266 and NK 400; the inhibition of the respiration of Staph. aureus chiefly depends on the halogen and acid radical, though depends somewhat on the alkyl radical. 2. Of the pentamethin cyanine group dyes, NK 74 (3, 3'-diethl-10-chlor-2, 2'-pentamethine rhiocyanine-3-iodide) showed a stronger respiratory inhibition to Sal. typhi than Staph. aureus, and, in some concentrations, the dye somewhat accel erated the respiration of Staph. aureus. 3. Of the three nuclei group dyes, NK 19 (3, 3'-tri-n-hepthyl-4, 4', 4"-trimethyl) showed very much stronger inhi-bition to the respiration of Sal. typhi than NK 9 (1, 1', 1"-triethyl-11-lepidine-4, 4'-pentamethine quinocyanine-1, 1"-di-iodide). The respiration inhibitory action of this type of dyes seems to depend on rathes the number of carbon of alkyl radical than the difference of nuclei. Things were nearly the same as to Staph. aureus. 4. As for the respiratory inhibition of Styryl group dyes to Sal. typhi, NK 143 (2-(p-dimethylamino- styryl-4-methlthylthiazole-3-n-heptyl iodide) was ths strongest, and it decreased in the order of NK 612 (2- (p-hydroxy-styryl)-pyridine-l-n-octhyl iodide), NK 547 (2, 4-bis-(p-dimethylamino-styryl)-pyridine-l-etyl iodide) and NK 611 (2(o-hydroxy-styrl)-pyridine-1-n-octhyl iodid); fhe alkyl-heptyl radical plays the most important role in the respiratory inhibition, and the presnce of some accelerationg factor is also inferred. To the respiration of Staph. aurens. NK 573 (2.6-bis-(p-dimethylamino-styryl)-pyridine-1-methyl acetate) showed very much stronger inhibition than NK 547; this fact suggests that CH(3)COO has big influence. 5. Of the aminovinyl group dyes, NK 122 (2-(w-anilino) vinyl-4-methlthiazole-3-n-hepthyl iodide) showed somewhat stronger inhibition to the respiration of Sal. typhi than NK 344 (2-(w-5'-bromo-2'-pyridyiamino)-vinyl-4-methyl thiazole-3-n-hepthyl iodide). NK 344, however, showed stronger respiratory inhibition to Staph. aureus than Sal. typhi.