<jats:p> Cephalosporin production by <jats:italic>Streptomyces clavuligerus</jats:italic> is regulated by some type of carbon catabolite control. Increasing concentrations of preferred carbon sources, such as glycerol and maltose, decreased production of the antibiotics. Poorer carbon sources, such as α-ketoglutarate and succinate, led to high specific production of cephalosporins and shifted the dynamics of fermentation to a greater degree of association with growth. The results support the concept that the phase in which a product is made by a microorganism is not a function of the particular molecule produced, but rather of the nutritional environment presented to the organism.