Luminescence has been detected in cyclic tetrapeptide disulfides containing only nonaromatic residues. Excitation of the -S-S- n-σ ∗ , filled transition between 280 and 290 nm leads to emission in the region 300-340 nm. The position and intensity of the emission band depends on the stereochemistry of the peptide and polarity of the solvent. Quantum yields ranging from 0.002 to 0.026 have been determined. Disulfide luminescence is quenched by oxygen and enhanced in solutions saturated with nitrogen. Contributions from disulfide linkages should be considered, when analysing the emission spectra of proteins, lacking tryptophan but having a high cystine content.