Scanning photometer microscopy was used to study wool fiber cross sections containing ultraviolet (UV) absorbers and optical brightening agents. Protein fiber wool absorbs in the UV range of the spectrum at 275 nanometers. This limits the application of UV microscopy on wool to the detection of UV-active textile finishing agents. Sulfonated UV absorbers can be detected by the transmitted light technique, and their migration in the wool fiber can be studied. Fluorescence microscopy can localize fluorescent or nonfluorescent textile finishing agents or polymers on wool after selective staining. The uptake by wool of fluorescent mothproofing agents, surfactants, or whitening agents can be investigated with this technique.