This study examined the effects of growth hormone (GH) replacement on the insulin-like growth factor-I (IGF-I), body composition and psychological profiles of GH-deficient adults. We assessed whether two doses of GH produced different effects on these variables and whether patients who, at the end of the study chose to remain on long-term GH replacement responded differently to those who chose to abandon therapy. Forty-two adults (aged 42.9 +/- 1.9 years (mean +/- S.E.M.)) with documented GH deficiency entered two studies (24 in study 1, 18 in study 2). Biochemical, body composition and psychological profiles were assessed at baseline, and after 6 months and 1 year. Psychological assessments were performed using well-established, independent, validated 'Quality of Life' questionnaires (Nottingham Health Profile (NHP) and the Psychological General Well-Being Schedule (PGWB)). The study protocols differed only in the doses of growth hormone (0.024 mg/kg per day and 0.012 mg/kg per day respectively). Comparison between studies and between patients eventually continuing and abandoning GH therapy was performed. GH replacement was associated with significant changes in IGF-I levels (P < 0.001), body composition (P < 0.01) and self-perceived well-being (NHP, P < 0.01; PGWB, P < 0.01). The higher dose of GH produced a greater IGF-I response than the lower dosage (44.6 +/- 7.3 vs 26.2 +/- 3.6 nmol/l, P < 0.05), but no better psychological response (NHP, P = 0.22; PGWB, P = 0.23). Those deciding to continue replacement therapy did not respond differently to those choosing to abandon therapy with respect to IGF-I (P = 0.72), body composition (P = 0.38) and psychological assessment (NHP, P = 0.29; PGWB, P = 0.24). GH replacement in GH-deficient adults was associated with significant improvements in self-perceived well-being as well as changes in body composition and other variables. This improvement was similar at two different doses of replacement GH. Those patients electing to continue on long-term replacement did not achieve a demonstrably different psychological, body composition or biochemical benefit to those patients deciding to discontinue replacement.