It is commonly stated that insulin antibodies (IA) cause insulin resistance. This is illogical as once insulin binding has reached equilibrium, the daily dose will circulate as free hormone. In order to pursue this question we studied three groups of patients: 30 patients treated with ‘dirty’ beef insulins over many years (Group l), 50 young patients who had received only porcine insulin (Group 2) and 12 patients with clinical ‘insulin resistance’ — requiring more than 150 units of insulin per day (Group 3). Insulin antibody binding was measured in a direct binding IgG class specific ELISA, and plotted against both the total daily insulin dose and the daily dose/kg body weight. Metabolic control did not differ significantly between the first two groups, but mean IA titre was significantly higher (p<0.001), and mean insulin dose significantly lower (p<0.001) in group 1 than group 2. There was no correlation between IA titre and either total daily insulin dose or dose/kg body weight. IA titre in the group with clinical insulin resistance was significantly less than in group 1 (p<0.05). We conclude that insulin antibodies do not cause insulin resistance.