The inosine synthesis by Bacillus subtilis mutants selected by the Institute of Genetics 265 and 21 and their development on the mineral medium were studied. The mutants behaved differently towards the sources and concentrations of carbon, nitrogen, phosphorus and magnesium as well as towards additions of tyrosine, histidine, adenine and uracyl. Optimal concentrations of the components of the mineral medium for the inosine synthesis by the Bac. subtilis mutants were determined. Under favourable conditions the mutants synthesized 8 to 10 mg/ml inosine for 120 hours.