We evaluated the clinical significance of the plasma TGF-beta 1 by enzyme-linked immunosorbent assay (ELISA) in 40 patients with gastric carcinoma before operation who were hospitalized at our department between August 1992 and March 1993. Moreover, we examined the correlation of the immunosuppressive acidic protein (IAP) in the serum with the plasma TGF-beta 1 level. The lymphocyte subsets were analyzed with monoclonal antibodies (CD3, CD4, CD8) and compared with the plasma TGF-beta 1 level. Results 1) The plasma TGF-beta 1 was significantly high in patients with advanced stage of gastric carcinoma (with respect to the depth invasion) and poorly differentiated adenocarcinoma (histological type) (p < 0.01). When the carcinoma was macroscopically found to be advanced, TGF-beta 1 was higher in the invasive type than in the noninvasive type (p < 0.05). 2) We found a significant correlation between the plasma TGF-beta 1 and IAP in the serum (n = 25, r = 0.677, p < 0.01). 3) The lymphocyte fraction of CD3, CD4 was decreased in patients with a high level of TGF-beta 1, and was related with the plasma TGF-beta 1 level. Thus, TGF-beta 1 was presumed to be deeply associated with in the growth and progression of gastric carcinoma and related to systemic immunosuppressive reaction.