Glutathione blood levels were determined in colorectal cancer patients (n = 10), patients with adenomatous colorectal polyps (n = 8), and healthy subjects (control group; n = 10). Mean GSH level (micrograms/ml) was significantly higher in cancer patients [515.4 +/- 76.1 (S.D.)] than in those with polyps [407.7 +/- 90.5 (S.D.), P less than 0.05] and the control group [360.9 +/- 67.9 (S.D.), P less than 0.001]. Statistically significant lower GSSG blood level were observed in cancer patients when compared to the other groups. The highest mean blood GSH/GSSG ratio (log transformed) was observed in cancer patients [2.17 +/- 0.108 (S.D.)] and the lowest in healthy subjects [1.88 +/- 0.032 (S.D.)]. All between-group differences in the GSH/GSSG ratio were statistically significant. These findings suggest that glutathione blood levels as well as GSH/GSSG ratio may have applicability as a guide for following the activity of colorectal diseases.