Plasma gastrin has been reported to be elevated among patients with colorectal cancer. The objectives of the present study were to confirm this observation and, if confirmed, to shed light on the reason for the elevation. Presurgical and postsurgical fasting plasma gastrin levels were compared between 24 patients hospitalized for colorectal adenocarcinoma resection and 25 control patients hospitalized for other surgery. Elevated presurgical gastrin levels in the case group that fell after surgery would be consistent with production of gastrin by the tumor. High presurgical gastrin levels in the case group that did not change following surgery would be consistent with excess gastrin production by G cells. The mean presurgical gastrin levels were 21.9 +/- 3.7 pM (cases) and 45.1 +/- 18.0 pM (controls). The mean postsurgical gastrin levels were 20.5 +/- 3.9 pM (cases) and 43.4 +/- 14.6 pM (controls). These results do not provide support for the hypotheses that gastrin is elevated in colorectal cancer patients or that gastrin is secreted by colorectal tumors in sufficient quantities to be measurable in the plasma.