Spectrophotometric determination of the ionophore compounds and mass spectrometry of the biosynthesis products revealed that the cells of Streptomyces chrysomallus subsp. macrotetrolidi during the lag phase permanently contained practically constant though insignificant (about 20 to 40 nmol/mg of protein) amounts of biosynthetic precursors of macrotetrolides, oligomers of nactinic acids. The oligomers of nactinic acids had antibiotic activity and in an amount of 2.5 micrograms/ml inhibited the growth of Bacillus mycoides. The oligomers of nactinic acids had ionophore properties and were highly labile with respect to inorganic cations. The presence of sodium in the extragent stabilized the calcium monomer, a trimer of nonactinic acid, and promoted washing off the substances of the nactinic nature from the cells. The cations of ammonia and possibly potassium stabilized the dimer and tetramer of nonactinic acid forming a more hydrophobic complex by comparison with the initial compounds.