Plasma concentrations of osteocalcin (OC) were studied in 40 chronic alcoholic men (age range: 21-56 years) before and after 3 weeks of ethanol withdrawal therapy and in 50 non-alcoholic controls selected in respect to age and sex. Plasma OC level in alcoholic subjects was significantly lower than in the controls (3.0 +/- 2.6 micrograms/l and 4.7 +/- 2.8 micrograms/l, respectively). After 21 days of withdrawal therapy, plasma OC level was significantly higher than at the day of admission (5.8 +/- 3.5 micrograms/l, P < 0.001). This level was not statistically different from that of the controls. We also demonstrated that the hydroxyapatite binding capacity of plasma OC before as well as after the withdrawal period was not different from that of the controls. The acetaldehyde adduction of purified bovine OC in vitro did not change any of its immunoactivity and hydroxyapatite binding capacity. The results emphasize the fact that the decrease of plasma osteocalcin in chronic alcoholics is reversible within 3 weeks of alcohol withdrawal and that the circulating protein seems to be similar to that present in controls.