5,5-Diethylbarbituric acid (barbital) stimulates the production of anthracycline antibiotics called galirubins in Streptomyces galilaeus in dependence on the strain, concentration and cultivation conditions. The stimulation is more pronounced (up to 300%) in the low-producing strain than in the production mutant. Under conditions of limited aeration the effect of barbital is increased in both strains. In the production strain barbital narrows the spectrum of metabolites produced. Higher barbital concentrations inhibit growth of the mycelium of both strains and decrease the formation of free anthracyclinones.