Fifty-one dogs (27 diabetic dogs, four that had recovered from diabetes and 20 healthy control dogs) were given 0·5 or 1·0 mg glucagon intravenously. Blood samples were taken before the injection and 10 and 20 minutes after it. Samples were analysed to determine C-peptide, insulin and glucose concentrations, and one sample from each dog was analysed for fructosamine. The median (interquartile range) concentrations of C-peptide in the samples taken at 10 minutes were 0·5 (0·3 to 0·8) nmol/l in the control dogs, 0·1 (0 to 0·2) nmol/l in the diabetic dogs, and 0·3 (0·2 to 0·4) nmol/l in the dogs that had recovered from diabetes. Seven of the 51 dogs showed mild adverse reactions after the injection of glucagon.