Streptomyces clavuligerus NRRL 3585 grown in a chemically defined medium containing glycerol as the sole carbon source transported this molecule by two different systems. One of these was constitutive with a very low uptake efficiency and insufficient to attend to the metabolic requirements of this bacterium (constitutive glycerol transport system) and the other (glycerol transport system (GTS)) active and specifically induced by o-glycerol which is responsible for the transport of more than 90% of the glycerol taken up the cells. GTS was seen to have an optimal pH and temperature of 7.0 and 30°C, respectively, and its Km was 14μM. It was repressed by L-serine and addition of this amino acid to the culture broth (10mM) inhibited the growth of S. clavuligerus but not that of other species of Streptomyces.