Acute pancreatitis may be complicated by acute lung injury associated with increased vascular permeability to plasma protein. The pulmonary accumulation of the plasma protein transferrin, radiolabelled in vivo with indium-113m, was monitored using a portable probe radiation detector in sixteen patients with acute pancreatitis. Plasma protein accumulation (PPA) indices were within normal limits (< 0.5 .times. 10-3 min) in all survivors (n = 10) and elevated in all but one of the non-survivors. All non-survivors had severe acute pancreatitis as judged by standard criteria. Thus increased lung vascular permeability was not a constant feature of uncomplicated acute pancreatitis and was only observed in patients with multisystem failure accompanied by clinically evident acute lung injury.