Patients with chronic liver disease (CLD) may show an abnormal glucose tolerance test (GTT). On the other hand, it is debated whether diabetics may undergo abnormalities of liver function. The aim of our study was to see whether galactose tolerance test (GaTT) is a suitable complementary diagnostic tool in defining the glucose metabolism abnormalities characteristic of the two above mentioned clinical entities. Thirty-one patients with CLD, 16 adult diabetics and 12 healthy volunteers were considered. GTT with radioimmunoassay of plasmatic insulin (IRI) and oral GaTT were performed. CLD patients were divided into two groups: with IRI/glycemia greater than 0.4 or less than 0.4. On GaTT, galactosemia was significantly raised in CLD compared to diabetics and control. Further, a statistically significant difference was shown in the glycemic variations during GaTT between diabetics and both CLD groups. A significantly inverse ratio galactosemia/glycemia occurred during GaTT and showed a different pattern between diabetics and CLD patients with impaired insulin secretion. A careful study of galactosemia and glycemia variations during GaTT reliably defines the different patterns of glucose metabolism derangement in CLD with abnormal GTT and in diabetics.