A case of well-differentiated adenocarcinoma (Borrmann type 3) of the stomach in a 76-year-old man associated with the typical skin manifestations of acanthosis nigricans and with multiple protruding lesions showing epithelial hyperplasia of the esophagus is reported. The advanced tumor was located in the cardiac region of the stomach, and measured approximately 8 cm in diameter, with partial invasion to the esophagus. The associated cutaneous lesions were characterized by hyperpigmentation and by protruding verrucous papules on the torso, head, face, neck, upper extremities, perineum, and inguinal region. Histologically, the protruding skin lesions showed keratinocytes proliferation throughout the epidermis, resulting in diffuse hyperkeratosis, papillomatosis, and acanthosis of the skin. Immunohistological analysis showed coexpression of transforming growth factor alpha (TGF-alpha) and epidermal growth factor (EGF) receptors in the tumor from the stomach. It is reasonable to conclude from this evidence that gastric carcinoma cells secrete TGF alpha in an autocrine for auto-stimulation. EGF receptor expression was also noted on the papillomatous hyperplasia of the cutaneous lesion. Serum level of TGF alpha, determined by an enzyme-linked immunosorbent assay, was high (144 pg/ml; normal, 22.0 +/- 16 pg/ml (Mean +/- SD)). Serum TGF alpha abruptly decreased to 49 pg/ml on day 7 after the total gastrectomy, and then gradually increased to 77 pg/ml within 28 days. Amelioration of the cutaneous lesions and the protruding lesions in the esophagus was observed after surgical resection of the gastric carcinoma. This suggests that the TGF alpha stimulates the proliferation of keratinocytes involved with EGF receptor. Large amounts of circulating TGF alpha in the blood over a long period released by the primary tumor seem to act as an endocrine-like mechanism causing epidermal and esophageal epithelial cells to proliferate. There is a possible link in the pathogenesis of the acanthosis nigricans as a cutaneous paraneoplastic syndrome, and epithelial hyperplasia of the esophagus.