Oral glucose (75 g) tolerance tests were performed on 189 urbanized Micronesians with an age range of 15 to 70 years. The subjects were divided into 6 groups on the basis of the 2 h plasma glucose and the pattern of insulin response examined. Fasting plasma insulin levels were not significantly different over the entire range of glucose tolerance. The 2 h plasma insulin levels were highest in the group with 2 h plasma glucose value of 140–199 mg/100 ml. There was a progressive fall in 2 h plasma insulin with increasing glucose intolerance, so that in the group with a 2 h plasma glucose ⩾ 400 mg/100 ml, the 2 h plasma insulin level was significantly less than that in all the other groups. Obesity was the most important factor influencing both fasting and 2 h insulin levels and no effect of corresponding plasma glucose level was demonstrated. In maturity-onset diabetes, a wide range of insulin responses may be seen and the earlier controversy regarding patterns of insulin response has arisen from equating groups of diabetic subjects with varying degrees of glucose intolerance.