<jats:p> Chloramphenicol production was studied in cultures of Streptomyces venezuelae growing in a simple buffered medium with ammonia as the nitrogen source and glucose, lactose, or a glucose–lactose mixture as the sole source of carbon. With each carbon source the antibiotic was formed during growth. In the glucose–lactose medium, the production pattern was biphasic; a marked decrease in the rate of synthesis was associated with depletion of glucose from the medium and a corresponding diauxie pause in growth. Cells of S. venezuelae contained an inducible β-galactosidase. Induction by lactose was suppressed by glucose. Measurement of the concentration of intracellular adenonsine 3′,5′-cyclic monophosphate during growth of cultures with glucose or a glucose–lactose mixture as the source of carbon showed no appreciable changes coinciding with depletion of glucose or the onset of chloramphenicol biosynthesis. It is concluded that the cyclic nucleotide does not mediate selective nutrient utilization or control antibiotic biosynthesis in this organism.