The authors studied the lipid profile in acute pancreatitis in humans and also in dogs in which this disease had been induced experimentally. Blood samples were analysed by mass spectroscopy and gas chromatography. During the acute phase of the pancreatitis there was a significant reversal of the ratio of unsaturated fatty acids. There was a marked increase in the concentration of fatty acids in the blood with monounsaturation in both carbon-16 and carbon-18 chains and diunsaturation in the later carbon chains. These changes have not been reported in any disease state.