Transforming growth factors beta (TGF beta s) show pleotrophic functions in vitro and in vivo. Biological effects depend on the cell type, the TGF beta isoform, and the availability of active TGF beta. Bioassays for TGF beta have not proven to be reliable tools in the measurement of TGF beta in human blood samples. Previously described sandwich ELISAs for measuring TGF beta are limited to single TGF beta isoforms and have not been evaluated for use in human sera or plasma. We describe a simple procedure to quantitate not only TGF beta 1 but also TGF beta 2 in human blood samples using commercially available antibodies. The sensitivity of the TGF beta 2 ELISA was 11 pg/ml. There was no crossreactivity between the TGF beta 1 and TGF beta 3 isoforms. High concentrations of TGF beta 1 and TGF beta 3 in spiked samples did not interfere with TGF beta 2 determination. TGF beta 2 recovery was highest in EDTA plasma (> 88%), and the intra- and interassay variance was 6% and 8.5% respectively. Applying the ELISA to human plasma specimens a significant percentage of TGF beta 2 (3.7 +/- 0.8 ng/ml) was found (about 50% of the TGF beta 1 content).