SUMMARY Plasma cyclic AMP levels were determined during a 40 minute secretin infusion (1 Cl.U kg-lh-1) followed by a 40 minute combined secretin (1 Cl.U kg-lh-1) caerulein (75 ng kg-lh-1) infusion. In nine healthy subjects, both secretin alone and secretin in combination with caerulein did not affect plasma cyclic AMP levels. (Levine, 1970;Kimberg, 1974).As the release of cyclic AMP to extracellular compartments and blood is proportional to intracellular concentrations (Taylor et al., 1970;Williams et al., 1972), it is reasonable to expect that variations in Abbreviations Cyclic AMP: adenosine 3':5'-cyclic monophosphoric acid; cyclic GMP: guanosine 3':5'-cyclic monophosphoric acid."Address for correspondence: Dr Jean Christophe, Department of Biochemistry and Nutrition, Free University of Brussels Medical School, Boulevard de Waterloo 115, B-I000 Brussels, BelgiumReceived for publication 24 October 1977 plasma cyclic AMP may reflect the response of target tissues to hormone administration.The control of the exocrine pancreas by cholecystokinin-pancreozymin and by an analogue such as caerulein is probably different and includes transient rises in calcium efflux and guanosine 3':5'-cyclic monophosphate levels. Data supporting this mechanism have been documented in rat and guineapig (Robberecht, 1976;Christophe et al., 1976) but has not yet been investigated in man.The initial purpose of the present study was to explore the possible usefulness of plasma cyclic AMP determinations during secretin and caerulein infusions as a further pancreatic function test. It became evident, however, that the data obtained were more useful in evaluating hepatic rather than pancreatic impairments. Methods SUBJECTSThirty-one adult patients were studied (21 males and 10 females). They were referred to the hospital for a 214 on 4 April 2019 by guest. Protected by copyright.