Since immunological and hereditary factors may be important in chronic pancreatitis, histocompatibility antigens of classes I and II were studied in 50 British Caucasian patients, after exclusion of insulin-dependent diabetics for whom HLA associations are recognised. Chronic pancreatitis was defined by at least two independent criteria, and only subjects with alcohol-related and idiopathic disease were included. In 22 patients (21 male), weekly ethanol intake had chronically exceeded 100 g (usually substantially so); the remaining 28 had idiopathic chronic pancreatitis (ICP). Twenty patients (40%) had autoantibodies, in 11 (22%) to gastric parietal cells. Nine of those with ICP (three male) had parietal cell antibody, more than expected for the age/sex distribution. There were overall increased frequencies of HLA Cw5 and B44. In ICP there were increased frequencies of HLA A25 and Cw1, and a decreased frequency of B7. In patients with alcohol-related disease there were increased frequencies of Cw5 (50.0% vs control 15.9%), B44 (54.5% vs 29.4%), and DR4 (61.1% vs 33.6%). The increased frequency of Cw5 in alcohol-related disease alone remained significant after correction (p less than 0.05). A hypothesis that hereditary and possibly immunological factors may contribute to the aetiology of chronic pancreatitis is supported.