THE AIM of the investigation was to study effects of extra low doses (10⁻¹⁰ – 10⁻¹⁴ mol/l) of 20 coded amino acids and their metabolites on the development of organotypical culture of rat testes. MATERIAL AND METHODS. The testes of 3 months old Wistar rats were divided into explants (1 mm³ fragments). The explants were placed in a Petri dish onto collagen and cultured in a CO₂-incubator in nutrient medium. Three days later the growth zone consisting of Leydig cells, Sertoli cells and spermatozoa was formed. For a quantitative assessment the area index was determined as the ratio of the total explant area to the central zone area. RESULTS. Reliable effects on the area index more than in one concentration was noted in 6 out of 20 coded amino acids: isoleucine (31±6%), lysine (25±4%), arginine (26±5%). None of the structural analogues of isoleucine (leucine, norleucine, valine) proved to be similarly effective. From all metabolites of L-arginine the testes growth is stimulated by L-ornitine (26±4%), urea (31±4%), creatine (20±3%); and L-citrulline (22±3%); and inhibited by nitric oxide (nitroglycerine – 100%). Glutatione eliminates antiproliferative effects of nitric oxide (25±7% vs 13±3% in concentration 10⁻¹³ mol/l) and thus increases effectiveness of L-arginine. In forming the mixture of the most active amino acids the arginine concentration must be 10 times more than the concentration of L-ornitine and creatine, but 10 times less that the concentration of L-lysine, L-isoleucine and L-citrulline. CONCLUSION. L-isoleucine, L- arginine and L-lysine are the most perspective amino acids for treatment of male infertility in clinical practice. It was first proved that L-isoleucine is maximally active for growth of testes. Nitric oxide is the only L-arginine metabolite with antiproliferative effect. A combination of L-arginine with glutathione eliminates the toxic effect of nitric oxide. A share correlation of amino acids necessary for maximal stimulation of the testes is established.