BACKGROUNDS: Transforming growth factor-beta1 (TGF-beta1) is a multifunctional polypeptide, promoting angiogenesis and accumulation of an extracellular matrix while inhibiting growth of epithelial cells and immune cells. Increased production of TGF-beta1 may be significant in the progression of cancer because it may result in an increased blood supply to the tumor mass and inhibition of immunologic mechanisms involved in tumor identification and cytolysis. However, little is known about the association of TGF-beta1 with progression of malignant disease in vivo. METHODS: Serum TGF-beta1 levels were measured in 100 patients with colorectal cancer and in 31 normal healthy volunteers used as control subjects. We used an enzyme-linked immunosorbent assay (ELISA) for the detection of serum TGF-beta1. RESULTS: The serum TGF-beta1 levels in the patients with colorectal cancer (40 9 ng/ml, n=100) were significantly higher than those in the control subjects (33 4 ng/ml, n=31)(p<0.001). The serum TGF-beta1 levels were 31 4 ng/ml in Dukes A (n=11), 38 9 ng/ml in Dukes B (n=31), 40 8 ng/ml in Dukes C (n=39), 48 8 ng/ml in Dukes D (n=19). These values, except for the Dukes B and Dukes C patients, were significantly different (p<0.01). The serum TGF-beta1 levels in patients with colorectal cancer increased with increasing tumor size (p<0.01). Simultaneous measurements of CEA and TGF-beta1 significantly increased the percentage of positive serum (72%) as compared with a single measurement. Elevations of the percentages of positive serum were revealed in Dukes A (27%), B (74%), C (72%) and D (94%). CONCLUSIONS: These results suggest that serum TGF-beta1 levels in patients with colorectal cancer may be associated with disease progression and may be of value in the management of patients with colorectal cancer.