OBJECTIVES: Specific problems in patients with insulin-dependent diabetes mellitus (IDDM) and GH deficiency are hypoglycaemic attacks, increased insulin sensitivity and loss of energy. These problems may be related to GH deficiency. PATIENTS: GH replacement was initiated in five patients with type 1 diabetes mellitus and GH deficiency for 6 months [four males and one female, mean age 41.6 +/- 3.8 years, mean +/- standard error of the mean (SEM); body mass index (BMI) 22.3 +/- 1.2 kg/m2]. METHODS: Body composition (bioimpedance), metabolic control [haemoglobin A1C (HbA1C)], insulin requirement and frequency of hypoglycaemia were measured, and quality of life was assessed using validated questionnaires. Monthly eye photographs were taken. RESULTS: IGF-I concentrations were below the age-adjusted range at baseline and increased significantly following GH replacement therapy [analysis of variance (ANOVA), P < 0.05]. Diabetes control as assessed by HbA1C remained stable (8.2 +/- 0.2 vs. 8.0 +/- 0.4), but needed a 1.75-fold increase in insulin dose/day. Lean body mass tended to increase (P = 0.07) and body fat mass decreased significantly (P > 0.01). Number of severe hypoglycaemic (< 3 mmol/l) attacks decreased significantly (P < 0.04) and quality of life assessed by validated questionnaires improved significantly in all patients [Psychological and General Well-Being Schedule (PGWBS), P < 0.04; Nottingham Health Profile (NHP), P < 0.05]. Monthly eye photographs revealed no changes in the retina in any patients. CONCLUSION: GH replacement therapy has a beneficial effect at the dose used. It restores body composition and decreases frequency and severity of hypoglycaemic episodes, thus improving quality of life. Long-term trials are needed to determine the safety of GH replacement therapy in these patients.