Calcofluor/Cellufluor (CFW) binds to fungal cell walls and causes them to fluoresce blue-green when illuminated with UV light. Retrospective and prospective studies were made to determine if CFW could be added to the Papanicolaou (PAP) stain procedure without altering diagnostic cytopathologic features while still allowing fungi to be identified. The retrospective study included 136 cytology specimens that were designated positive for fungus by PAP stain; these were stained with a 0.1% aqueous solution of CFW and examined by fluorescent microscopy. The overall agreement between the two methods in the detection of fungi was 90.4%. The incorporation of CFW into the PAP stain was tested at various points in the PAP stain sequence; optimum results were obtained when CFW was introduced after acid eosin. A total of 197 random, sequentially accessioned cytology specimens were stained with the PAP/CFW combination in the prospective study. The results indicate that detection of fungi by a combination of regular light and fluorescent microscopy was far more effective than was examination for the organisms by light microscopy alone.