The optimal concentrations of mineral phosphorus for the growth of the tobramycin-producing organism and for the production of the antibiotic by it in the synthetic medium were determined. Introduction of an additional source of mineral phosphorus into the rich soybean medium resulted in decreased levels of antibiotic production. The stimulating effect of manganese sulfate on the biosynthesis of tobramycin in the rich medium was shown. The stimulating effect of soybean, linseed and palm oils on the production of tobramycin was evident when the fermentation period was longer.