SummaryobjectiveWe examined the contributions of growth hormone (GH) and Insulin‐like growth factor‐I (IGF‐I) to Insulin sensitivity and beta‐cell function in acromegaly.designA cross‐sectional study was used with continuous Infusion of glucose with model assessment todetermine Insulin sensitivity and beta‐cell function.patientsTen patients with active acromegaly, seven with controlled disease and 22 normal Individuals werestudied.measurementsGlucose and insulin levels were measured fasting and at the end of the one‐hour glucose Infusion to calculate insulin sensitivity and beta‐cell function. Random GH and IGF‐I were recorded. Most patients had values of GH taken after a 100‐g oral glucose tolerance test and K values from Intravenous glucosetolerance tests.resultsPatients with active acromegaly had significantly decreased Insulin sensitivity compared to thenormal population (P<0·001), while those with controlled disease did not. There was a significant negative correlation between IGF‐I and insulin sensitivity In those with active disease (P<0·05). Beta‐cell function in both active and controlled patient groups was elevated compared tothe normal population (P<0·05,P<0·01 respectively) and this was significantly related to IGF‐I in the active group (P<0·05). GH levels did not correlate with fasting Insulin, glucose, Insulin sensitivity or beta‐cell function In either group.conclusionsPatients with active acromegaly have decreased insulin sensitivity and Increased beta‐cell function that are significantly related to IGF‐I but not GH levels. When the disease is controlled, beta‐cell function remains ele