Dissolving basic peptides such as insulin, secretin, and somatostatin in albumin-containing solutions increases the biologic potency. As CCK-33 also constitutes a basic peptide, it should have similar qualities. In four conscious dogs with chronic gastric and pancreatic Thomas fistulas, we studied the effect of CCK-33 solutions with and without addition of albumin on pancreatic secretin, plasma PP concentration, CCK-like immunoreactivity in plasma and infusion lines. The response of pancreatic protein output (mg/15 min) to increasing doses of 99% pure CCK-33 (0.5; 1; 2; 4 IDU/kg/h) was significantly higher (p less than 0.05) when CCK was dissolved in 0.154 M NaCl with albumin than in NaCl alone. These results were confirmed by measuring plasma CCK-immunoreactivity by CCK-RIA and CCK-immunoreactivity in samples from tips of infusion lines by gastrin-RIA. CCK evoked PP release at increasing doses of CCK-33, which was significantly (p less than 0.05) higher when CCK was dissolved in an albumin-containing solution. There was a significant (p less than 0.02) correlation between plasma PP concentration and pancreatic protein output. Our study shows addition of albumin to solutions of CCK-33 to cause an increase of CCK-33 activity, probably by preventing adsorption of the peptide to glass and plastic surfaces. This is valid for its effect on pancreatic protein secretion as well as PP release.