Streptomyces viridosporus strain T7A was grown in a mineral medium supplemented with glycerol (0.7%) and lignosulfonate (0.1%). The biodegradation of two different molecular sized lignosulfonates was studied. Determination of lignosulfonate concentration measured by the nitroso-method revealed that S. viridosporus degrades lignosulfonates differently according to their molecular size. Lignosulfonate losses were 10 and 25% for the higher and shorter molecular weights, respectively. Production of lignin peroxidase activity was induced by lignosulfonate and was growth-associated.