Recombinant follicle stimulating hormone (recFSH, Org. 32489) has been characterized by absorption (UV and IR), (polarized) fluorescence, linear-dichroism (LD) and circular-dichroism (CD) spectroscopy. Absorption and fluorescence spectra of the isolated subunits have also been measured. From the spectra the extinction coefficient, fluorescence quantum yield and anisotropy have been calculated. Global analysis is used to characterize the bands in the spectra. The adsorption, CD, LD and fluorescence excitation spectra all contain a band around 300 nm that appears to be a sensitive indicator for the intactness of the protein. Evidence is provided for the involvement of tyrosinate in the fluorescence, and for a close contact between the tryptophan (in the β subunit) with at least one tyrosine of the α subunit. The overall secondary structure of recFSH has been determined from its far-UV CD and its IR absorption spectrum. The secondary structure of recFSH is estimated to contain 15–25% α-helix, 15–25% β-turn and 30–40% β-sheet. The β-sheet in recFSH is almost exclusively antiparallel. The results confirm that recFSH contains significantly more α-helix than the closed related human glycoproteins, chorionic gonadotropin and lutropin; however, the α-helices may be short and distorted.