The alpha-amylase of Streptomyces sp. IMD 2679 was subject to catabolite repression. Four different growth rates were achieved when the organism was grown at 40 degrees C and 55 degrees C in the presence and absence of cobalt, with an inverse relationship between alpha-amylase production and growth rate. Highest alpha-amylase yields (520 units/ml) were obtained at the lowest growth rate (0.062 h(-1)), at 40 degrees C in the absence of cobalt, while at the highest growth rate (0.35 h(-1)), at 55 degrees C in the presence of cobalt, cr-amylase production was decreased to 150 units/ml. As growth rate increased, the rate of specific utilisation of the carbon source maltose also increased, from 46 to 123 mu g maltose (mg biomass)(-1) h(-1). The pattern and levels of alpha-glucosidase (the enzyme degrading maltose detected intracellularly in each case, indicate that growth rate effectively controls the rate of feeding of glucose to the cell, and thus catabolite repression.