Objective: Complex changes in the anabolic regulators of metabolism occur after major injury. We have studied the time course for IGF-I and IGFBP-1 after burn injury and their relations to circulating levels of other anabolic and catabolic hormones. The hormonal patterns during the onset of sepsis were also investigated., Patients: Eight patients (age 36 (6) years, mean (SEM)) with major burn injury (burn area 42 (6) %) were studied. The first 2 days since the burn were used for rehydration therapy (rehydration period), after which a complete total parenteral nutrition (TPN) period was initiated. Seven positive blood cultures, during the study period. Six of the eight survived., Measurements: The hormonal changes determined in the morning during the first 7 days after the burn and from day 22 to 24 were investigated. The superimposed effects of sepsis were studied by normalizing all data to the day of positive blood cultures and clinical onset of sepsis., Results: On admission, plasma levels of glucagon, IGFBP-1 and GH were elevated while levels of IGF-I were low. During the first week after the burn, morning levels of glucagon and insulin increased while levels of GH and IGF-I decreased. GH levels were still elevated compared to healthy subjects. Despite the increase in insulin levels, IGFBP-1 remained elevated. Three weeks after the burn injury, IGF-I levels were increased but still markedly below normal, while IGFBP-1 levels remained unchanged. Persistent elevations of insulin levels were combined with reductions in glucagon levels. Admission levels of IGFBP-1 correlated to nitrogen loss (negative nitrogen balance) during the first 24 hours after the burn (r = 0.84, P < 0.05). A correlation between negative nitrogen balance and glucagon levels was found during early catabolic period in the rehydration period (i.e. days 2-3, r = 0.84, P < 0.01). The relative change in IGFBP-1 levels in the rehydration period correlated to changes in glucagon levels (days 2-3 vs admission, r = 0.85, P < 0.05). The insulin/glucagon molar ratio correlated to the IGF-I/IGFBP-1 ratio during both the rehydration period (days 2-3, r = 0.77, P < 0.05) and the third week after the burn (r = 0.77, P < 0.05). During the most catabolic phase in the first week after the burn (TPN period) there was an inverse relation between IGF-I and IGFBP-I and glucagon (r = 0.83, P < 0.05). During the less catabolic third week after the burn, an inverse correlation was found between IGF-I and glucagon (r = -0.83, P < 0.05). Sepsis, superimposed upon the burn trauma, was associated with transient elevations in IGFBP-1 and reductions in insulin despite elevated levels of glucose and a further 50% increase in nitrogen losses., Conclusions: The present findings show that marked changes is important anabolic regulating factors occur after major burn injury. Uncoupling of the GH-IGF-I axis, and the attenuation of the inhibitory effects of insulin on IGFBP-1, both contribute to the reduction in IGF-I levels and bioavailability, factors which may play an important role in post injury metabolism. Furthermore, these data suggest that the catabolic hormones (catecholamines, cortisol and glucagon), primarily glucagon seem to be involved in the modulation of IGF-I and IGFBP-1 levels following burn injury.