We have investigated plasma glucose and insulin responses to 75 g glucose in 12 young, full-blood Aborigines before and after 2 weeks on a diet derived almost exclusively from seafood. This diet was low in fat, extremely low in carbohydrate and high in protein and was representative of the diet consumed by these people in their traditional lifestyle during those times of the year when very little vegetable food was available. After an initial weight loss which was probably due to glycogen, salt and water losses associated with the dietary change, body weights stabilised by the end of the first week. Total triglyceride concentrations in fasting plasma fell from 1.32 +/- 0.33 before the diet to 0.61 +/- 0.08 mmol/l after it, while total cholesterol, which was low initially, did not fall significantly. There was a small but significant improvement in glucose tolerance and a small reduction in insulin response indicating that the Aborigines had adapted effectively to the very low carbohydrate-high protein diet in the 2 week period. The insulin response to 50 g protein also fell significantly after the seafood diet. The results suggest that glucose tolerance is not determined solely by the carbohydrate content of the diet, but rather by the availability of carbohydrate either directly or indirectly in precursor form as dietary protein.