In four healthy volunteers increasing doses of intravenous CCK-33 induced an increase in plasma PP concentration measured by RIA. PP concentration rose from a basal level of 67 +/- 15 pmol/l to 198 +/- 45 pmol/l with 2 IDU/kg/h (p less than 0.05). In four mongrel dogs equipped with Thomas cannulas, the same doses induced a more pronounced rise in plasma PP (p less than 0.01). It is concluded that intravenous CCK-33 induces the release of PP in man and dog in a dose-dependent manner.