The natural medium contained the following ingredients (g/l): glucose 8.0, or black strap molasses (treated with 0.2--0.3 g/l EDTA) 12.0, fodder yeast (50.0% total nitrogen) 2.0, or folder yeast (40.0% total nitrogen) 6.0, or yeast extract 8.0, or tryptone 8.0, and CaCO3 1.0. Treated black strap molasses with EDTA and fodder yeast proved to be effective in the fermentative production of gentamicins. The most suitable chelating agent was EDTA in the form of disodium for the treatment of Komombo molasses in a concentration of 0.2--0.3 g/l, while potassium ferrocyanide and methylene blue had depressing effects on the production of gentamicins. The most effective carbon source, present in Egyptian black strap molasses, was glucose. Addition of glucose to the medium was preferable at the beginning of the fermentation process. Trace elements present in molasses were very essential for the microbial growth and biosynthesis of gentamicins as proved when molasses ash was added to the natural medium. Organic nitrogen sources were more suitable than inorganic nitrogen sources for the production of gentamicins by Micromonospora purpurea. The microorganism utilized the synthetic medium, but the antibiotic yields were less than those produced in the natural medium. The synthetic medium exhibited stimulatory effects of certain amino acids, organic acids, vitamins, and purine and pyrimidine bases on the fermentative production of gentamicins. Therefore, the ingredients increasing yields of gentamicins were mainly phenylalanine, iso-leucine, lysine, methionine, leucine, arginine, glycine, beta-alanine, cystine, tryptophan, malic acid, maleic acid, cobalamin, folic acid, riboflavin, vitamin B1, vitamin B6, biotin, nicotinamide, uracil, adenine, guanine, and adenosine. Trace elements (Co, Mo, Fe, Cu, Zn, and Mn) exhibited their important role on the biosynthesis and production of gentamicins by Micromonospora purpurea.