The composition of the fatty acids of the total lipids and its changes during culturing of Act. fluorescens, Act. globisporus, Act. viridis, Act. roseoflavus var Act. roseofungini and two of its proactinomycetes-like variants, were studied. The qualitative composition of the fatty acids of all the strains studied did not differ; the assortment of acids contained 11 basic components: C14-C18 acids-saturated, with normal, iso, and anteiso structures, and monoenic of normal structure. As the mycelium grows, the age dynamics of the fatty acids in submerged culturing are characterized by an increase in the total of saturated branched acids and a decrease in the total number of unsaturated acids. In the case of surface culturing, this tendency is maintained for vegetative cells; when aerial mycelium appears, the sum of the two components mentioned is unchanged. The level of normal saturated acids is constant.