The secondary structures of two recombinant human growth factors, platelet-derived growth factor and the basic fibroblast growth factor, have been quantitatively examined by using Fourier transform infrared spectroscopy. These studies, carried out in D2O, focus on the conformation-sensitive amide I region. Resolution enhancement techniques, including Fourier self-deconvolution and derivative spectroscopy, were combined with band fitting techniques to quantitate the spectral information from the broad, overlapped amide I band. The results presented here indicate that both proteins are rich in beta-structures. The remainder of the platelet-derived growth factor exists largely as irregular or disordered conformations with a moderate amount of alpha-helix and a small portion of reverse turns. By contrast, the basic fibroblast growth factor is much richer in reverse turn structures and contains a lesser portion of irregularly folded or disordered structures. Based on circular dichroism studies which indicate no alpha-helix in bFGF, components near 1655 cm-1 in the bFGF spectra are tentatively assigned to loops. The results of this study emphasize the need for using a combination of circular dichroism and infrared studies for spectroscopic characterization of protein secondary structure.