Metabolic effects of D-glucosamine on the pancreatic islet B-cells were evaluated by measurements of the oxygen uptake of isolated and surviving islets. The tissue specimens, which were obtained from obese-hyperglycaemic mice and consisted of more than 90% B-cells, were incubated in Cartesian divers with Krebs-Ringer phosphate medium at +37° C. Addition of glucosamine to the incubation medium caused a significant inhibition of the endogenous islet respiration and an even more pronounced inhibition of the oxygen uptake in the presence of D-glucose. When islets were pre-incubated with glucosamine and subsequently supplied with glucose, there was a relatively slight elevation of the oxygen consumption rate, indicating a partial block of the stimulating effect of glucose on the islet respiration. The results support the view that the diabetogenic effect of glucosamine is caused in part by a direct interference with the glucose utilization in the pancreatic B-cell, resulting in a diminished insulin release.