Somatostatin has been detected in the gastrointestinal tract and has been shown to have wide actions on gastrointestinal function. Using an isotope method with 51Cr as a stool marker, we have examined the absorption of 47Ca in 9 healthy volunteers with and without infusion of cyclic somatostatin (250 microgram/h for 2 hours). Both serum and faecal measurements show reduced 47Ca-absorption during somatostatin infusion, net absorption falling from 53.0 +/- 14% without to 40.4 +/- 13% with somatostatin. Possible explanations are discussed with special emphasis on the possibility of an inhibition of active calcium transport, which may be a more general mode of somatostatin action.