To determine whether a correlation exists between hormone receptors and their proliferative activities, the levels of estrogen receptors (ER) and progesterone receptors (PgR) in surgical specimens from 23 patients with gastric cancer and from 32 patients with colorectal cancer were investigated using an enzyme immunoassay. These values were examined in relation to the parameters of cell kinetics determined by DNA flow cytometry. When the cutoff value was determined as 2.0 fmol/mg of cytosolic protein, ER and PgR were found in 13 (56%) and 6 (26%) of the 23 patients with gastric cancer, respectively, and in 10 (31%) and 10 (31%) of the 32 patients with colorectal cancer, respectively. There was a significant correlation in the expressions of ER between the cancer tissues and normal mucosa (P = 0.040). Although the expressions of ER or PgR were apparently not related to pathological status, better correlations of hormone receptor-negative tumors with increased hyperaneuploid levels were evident. According to a multiple regression analysis, ER levels significantly correlated with changes in the DNA index (P = 0.041) and in the heterogeneity index score (HIS) (P = 0.034). Thus, sex hormone receptors proved to be relevant factors associated with the proliferative activity of adenocarcinoma of the gastrointestinal tract. These findings indicate that the expression of hormone receptors provides pertinent biological information required to determine adequate therapeutic regimens in patients with gastrointestinal cancer.