The influence of glucosamine, galactosamine, glucuronic acid and of some derivatives of these compounds on mucopolysaccharide metabolism and on protein metabolism of primary fibroblast monolayer cultures was studied. Glucosamine, glucosamine · HC1, glucosamine · HJ and glucosamine sulfate (in concentrations of 100 µg/ml each) caused a considerable, statistically highly significant increase of the secretion of mucopolysaccharides by the fibroblasts. N-Acetylglucosamine and N-acetylgalactosamine were effective too, though to a lesser degree. Glucuronic acid was without any influence on mucopolysaccharide production. The protein content of the cultures was not affected by the 7 compounds mentioned so far in concentrations of up to 100 µg/ml. Galactosamine and betaineglucuronate induced a certain depression of a mucopolysaccharide production and simultaneously a decrease of the cellular protein content.