We evaluated polyamine (putrescine, spermidine, and spermine) levels, estrogen receptor concentrations, and their relationship in neoplastic tissue and surrounding mucosa from 30 patients with gastric adenocarcinoma. Cytosolic estrogen receptors were measured with an immunoenzymatic assay. Polyamine levels were evaluated with high-performance liquid chromatography. Estrogen receptor concentrations were statistically higher in surrounding mucosa than in neoplastic tissue (p = 0.023). Putrescine and spermidine levels and the spermidine to spermine ratio were statistically higher in neoplastic tissue than in surrounding mucosa (p < 0.004). Significant correlations were found between the levels of spermidine and total polyamines in neoplastic tissue and surrounding mucosa (r = 0.48, p = 0.014, and r = 0.45, p = 0.021, respectively). Polyamine levels were lower in estrogen-receptor-positive tumors than in estrogen-receptor-negative ones, although this decrease was statistically significant only in the case of spermine (p = 0.02). The significance of these findings is that the cellular activity of normal and neoplastic gastric mucosa may be partly controlled by estrogens.