In 16 patients with acute viral hepatitis and 32 sex- and age-matched control subjects the serum levels of osteocalcin, a biochemical parameter of bone formation, as well as the serum levels of parathyroid hormone, 25-hydroxyvitamin D, calcium and phosphorus were measured. The serum levels of osteocalcin (P less than 0.0001) and parathyroid hormone (P less than 0.0001) were significantly lower when measured at the time of maximal aminotransferase levels in the patients with hepatitis than in the control subjects. In contrast, the serum levels of calcium and 25-hydroxyvitamin D were similar in the patients and the controls. In nine patients with acute hepatitis measurements of the biochemical bone metabolism parameters were performed after normalization of the liver enzymes. In these patients a significant increase of serum osteocalcin levels towards normal values (P less than 0.0005) was found, parathyroid hormone levels tended to increase. Our data suggest an alteration of bone metabolism in patients with acute viral hepatitis. Bone formation as reflected by serum osteocalcin levels seems to be decreased in acute hepatitis and returns to normal after recovery from hepatitis.