<jats:title>Abstract</jats:title><jats:p>The composition of fatty acids and the spectrum of macrolide antibiotics produced in 7 mutant strains of <jats:italic>Streptomyces fradiae</jats:italic>, 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 specifity of secondary metabolism enzymes, the composition of the tylosin‐like compounds produced can be influenced by the cell membrane and its function.