We investigated whether the concentration of circulating transforming growth factor beta (TGFbeta) yields diagnostic value in breast cancer. Blood was collected from twenty stage I and II breast cancer patients both prior to treatment and after surgical excision of the tumour. Both latent and active TGFbeta were quantified directly in the blood plasma using a bioassay. The average plasma TGFbeta level in breast cancer patients was 20.8 +/- 8.5 ng/ml (n=20; mean +/- SD), which was not different from normal controls. Elevated plasma TGFbeta levels (> average control +/- 2SD) were found in 5% (1/20) of the controls and in 25% (5/20) of the patients. Correlation was not found between plasma TGFbeta level and tumour type nor with tumour stage. Following surgical excision of the tumour, plasma TGFbeta levels were not significantly altered. Thus, our data show that plasma TGFbeta levels do not reveal diagnostic value for early stage breast cancer. Determination of the pretreatment plasma TGFbeta value of the individual patient might, however, still be meaningful since it appears to be predictive for its normal tissue reaction following cancer therapy.