The composition of fatty acids and the spectrum of macrolide antibiotics produced in 7 mutant strains of Streptomyces fradiae, a tylosin producer, were investigated. The strains under investigation differed in the production level and representation of individual tylosin-like compounds. The composition of fatty acids in the mycelium did not depend on the total production. However, the strains producing relomycin in addition to tylosin produced a significantly higher fraction of fatty acids with a higher melting point, and, on the contrary, the strains producing only tylosin or tylosin and desmycosin synthesized a significantly lower proportion of these acids. The results obtained indicate that in addition to the activity and substrate specificity of secondary metabolism enzymes, the composition of the tylosin-like compounds produced can be influenced by the cell membrane and its function.