Grey scale ultrasound scanning has been performed within 1 week of admission in 114 patients with acute pancreatitis in order to establish its reliability in detecting gallstones and to document early pancreatic changes. When the gallbladder was identified (69.4 per cent of patients), grey scale ultrasound was 96.1 per cent accurate in predicting the presence of gallstones. Of 85 patients (74.5 per cent), in whom adequate pancreatic imaging was achieved on the initial scan, 35 were reported within normal limits, 28 had generalized pancreatic swelling and 22 a localized pancreatic mass of cystic collection. These ultrasound findings did not correlate significantly with the objective assessment of severity of disease. However, all 9 patients (8.1 per cent) who developed a pseudocyst were in the group shown to have early localized pancreatic swelling. Grey scale ultrasound is a useful method of detecting gallstones in patients with acute pancreatitis, thus permitting early accurate biliary surgery. However, in almost one-third of our patients ultrasound failed to outline the gallbladder on the initial scan. While ultrasound scanning of the pancreas will detect the formation of pseudocysts and accurately chart their subsequent progress, we doubt whether an early scan is required to achieve this purpose. Although generalized pancreatic swelling is frequently reported, this finding was of no major clinical importance and did not relate to the severity of disease.