This is an exploratory trial with four cross-over arms measuring the pharmacokinetic and pharmacodynamic profiles of growth hormone using two different modes of growth hormone administration (subcutaneous infusion into the abdomen or subcutaneous bolus injection in the thigh) in 8 adult male or female patients with growth hormone deficiency during interval exercise or in supine rest. The order of dosing regimen within the groups and between the groups will be randomised. All patients will go through four different treatment sessions:A/B Single subcutaneous bolus injection, supine rest without/with interval exercise, sessions C/D: Continuous subcutaneous infusion, supine rest without/with interval exercise. Hypotheses: 1) There is day-to-day variation of exogenous growth hormone, 2)Concentration of growth hormone decreases due to exercise compared to supine rest, 3)There is a circadian variation in pharmacokinetics of exogenous growth hormone infused subcutaneously