Some indices of the kallikrein kinin system, namely kininase I (KI), kininase II or angiotensin converting enzyme (KII-ACE) and phenylalanine-arginine aminopeptidase (AP) were analyzed, to detect their levels in ten selected normal subjects and in 20 selected patients with colonic (n = 8) and gastric adenocarcinoma (n = 12). While AP and KI levels did not show differences in the groups under analysis, KII values showed a significant difference (P +/- 0.01), present since the early stages of the diseases and unrelated to the normal laboratory indices.