The effect of concentrations of organic acids in the cultural broth on growth was studied with the strains of Mycococcus lactis and Pseudomonas fluorescens oxidizing hydrocarbons. The ratio between the acid and neutral fractions in the cultural broth of Mycococcus lactis was also investigated as well as their action on the bacterial growth. Mycococcus lactis growing on paraffin was found to produce acid and neutral products at a ratio of 1:2. The acid and neutral products of metabolism produced different action on the growth of the carbohydrate oxidizing bacteria. The acid products inhibited the growth at a concentration of organic acids in the medium above 500 mg/litre. The neutral products were partily assimilated by Mycococcus lactis.