The light emission and the loss of cell viability observed when phenylacetaldehyde is added to neutrophils are greatly enhanced when phenylacetaldehyde is administered as a Schiff base with amino acids. As in the case of phenylacetaldehyde, the Schiff base undergoes an intracellular, myeloperoxidase-catalyzed, oxygen-consuming process. Sonication of the cells enhances the emission. With both the free aldehyde and the Schiff bases, the emission spectrum peaks in the 490 nm region, whereas optically excited neutrophils and spent reaction mixtures show maximal emission elsewhere. Apparently, the primarily formed excited species (triplet benzaldehyde) either specifically transfers excitation energy to a component that makes only a minor contribution to the luminescence spectrum of the cells or initiates a process which is itself emissive, e.g. lipid peroxidation. As in the case of phenylacetaldehyde, the oxidation of the Schiff bases excites chlorophyll taken up by neutrophils. Loss of cell viability is likely to be related to in situ generation of excited species.