Recent studies have demonstrated that growth hormone (GH)-deficient adults have a markedly decreased bone mineral content compared to healthy adults. However, there are conflicting results regarding the effects of GH treatment on bone mineral content in GH-deficient adults. Therefore, we evaluated the effect of GH treatment on a marker of bone formation (bone alkaline phosphatase), hepatic excretory function and distal forearm bone mineral content in GH-deficient adults. Growth hormone was administered subcutaneously in 21 adults (13 males and 8 females) with GH deficiency of childhood onset for 4 months in a double-blind, placebo-controlled GH trial, while 13 of the patients then received further GH for an additional 14 months. Serum insulin-like growth factor I (IGF-I) increased significantly from 100 to 279 micrograms/l and IGF binding protein-3 (IGFBP-3) from 1930 to 3355 micrograms/l after 4 months of GH treatment (p <0.0001). In addition, the molar ratio between IGF-I and IGFBP-3 increased significantly from 0.22 to 0.33 after GH treatment (p <0.0001). Bone alkaline phosphatase increased significantly from 38.6 to 92.9 U/l during GH therapy in male patients (p <0.0001), whereas liver-derived alkaline phosphatase was unaltered by GH. In the females, the increase in bone alkaline phosphatase did not reach statistical significance (19.1 vs 40.0 U/l, p = 0.06). The GH-induced increase in bone alkaline phosphatase correlated significantly with the increase in serum IGFBP-3 (r = 0.46, p = 0.04) but not with the increase in serum IGF-I (p = 0.16).(ABSTRACT TRUNCATED AT 250 WORDS)