Dye binding to Papanicolaou-stained cervical cells was quantitated with a spectral subtraction technique. It was shown that of the dye components of Papanicolaou stains only aluminum hematein, orange G, light green SF and eosin Y are bound to cervical cells and that their chromophores do not interact. Bismarck brown Y was not bound to cervical cells, which confirms the subjective findings of previous authors, and so it should be omitted. No evidence of substrate-related variations in dye polymerization was found. The proportions of the four dyes were found to vary considerably from substrate to substrate. Spectra are presented of (1) solutions of the component dyes of the Papanicolaou stain, and (2) cervical cells stained with these individual component dyes, for comparison with the full Papanicolaou technique.