Transforming growth factor-beta1 (TGF-beta1) is known as the growth factor that stimulates the synthesis of extracellular matrix. Recently, TGF-beta has been found to control the growth of cancer cells. Small chondroitin-dermatan sulfate (decorin) is an abundant extracellular matrix component. TGF-beta1 stimulates the synthesis of decorin, and decorin is considered to bind TGF-beta1. The activity of decorin in neutralizing TGF-beta1 activity suggests that decorin serves as a negative-feedback regulator of TGF-beta1 activity. To investigate the role and relationship of TGF-beta1 and decorin in the formation of central fibrosis in pulmonary adenocarcinoma, we performed an immunohistochemical study of TGF-beta1 and decorin in 61 cases of T1 pulmonary adenocarcinoma. Positive stainings for TGF-beta1 were shown in 40 cases and negative in 21 cases. Twenty-seven of 32 cases with central fibrosis were positive for TGF-beta1. Positive staining for TGF-beta1 was significantly related to the appearance of central fibrosis in pulmonary adenocarcinoma. When central fibrosis was composed of proliferative connective tissue with loose staining for decorin, cancer cells showed intense staining for TGF-beta1. When central fibrosis was composed of old fibrotic tissue with dense staining for decorin, cancer cells showed weak staining for TGF-beta1. Our results suggest that TGF-beta1 has an important role in the formation of central fibrosis in pulmonary adenocarcinoma, and decorin may play a role as a negative feedback regulator in the production of TGF-beta1 in pulmonary adenocarcinoma.