The purpose of this study was to investigate, by a prospective, self-controlled method, whether early treatment with carbamazepine monotherapy can alter bone metabolism in ambulatory epileptic children with adequate sun exposure, based on the determination of total serum alkaline phosphatase and its bone isoenzyme activities. Serum total alkaline phosphatase and its bone, liver, and intestinal isoenzyme activities were evaluated in 22 epileptic ambulatory children (13 males and 9 females, aged from 5 to 12 years) before and at 3, 6, and 12 months of carbamazepine monotherapy. Serum concentrations of other biochemical markers of bone and liver metabolism, such as calcium, phosphorus, magnesium, gamma-glutamyltransferase, alanine aminotransferase, aspartate aminotransferase, and lactate dehydrogenase, were also measured in the study participants before and at 6 and 12 months of treatment. Carbamazepine was prescribed at normal dosages (16.4-20 mg/kg/day). Serum total alkaline phosphatase activities were significantly increased at 3 (P = .000), 6 (P = .024), and 12 (P = .037) months of treatment; serum bone alkaline phosphatase activities at 3 (P = .000), 6 (P = .008), and 12 (P = .017) months of treatment; and serum liver alkaline phosphatase activities at 3 (P = .000), 6 (P = .049), and 12 (P = .008) months of treatment, whereas serum intestinal alkaline phosphatase isoenzyme activity was significantly increased only at 3 months of treatment (P = .035). Serum gamma-glutamyltransferase activities were also significantly increased at 6 (P = .000) and 12 (P = .000) months of treatment. No significant changes in the concentrations of serum calcium, phosphorus, magnesium, alanine aminotransferase, aspartate aminotransferase, and lactate dehydrogenase were noted at 6 and 12 months of treatment. There was a significant correlation between serum gamma-glutamyltransferase activities and serum total alkaline phosphatase activities (r = .689, P = .000 at 6 months; r = .493, P = .020 at 12 months), bone alkaline phosphatase activities (r = .700, P = .000 at 6 months; r = .466, P = .029 at 12 months), and liver alkaline phosphatase activities (r = .427, P = .047 at 6 months; r = .425, P = .048 at 12 months). These findings indicate that ambulatory children who receive carbamazepine monotherapy, even when residing in a country with adequate sunlight, can have their bone metabolism altered early in the course of treatment, as indicated by the elevated activities of serum bone alkaline phosphatase isoenzyme. This early alteration in bone metabolism is probably due to the hepatic enzyme-inducing character of carbamazepine.