This study sought to determine, firstly, the relative frequency of lymphocytes and macrophages and, secondly, the percentage of lymphocytes containing interferon‐γ in inflamed islets (insulitis) of patients with type 1 (insulindependent) diabetes. Autopsy pancreases of 12 patients who had died of recent‐onset type 1 diabetes and one prediabetic patient who had died of cardiomyopathy were examined immunohistochemically. In the 87 islets that were studied, the lymphocyte macrophage ratio was 9·7:1 and approximately 40 per cent of the lymphocytes contained interferon‐γ. Interferon‐γ release in the insulitis process may be involved in the pathogensis of type 1 diabetes.