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pH and CO2 fiber-optic sensors were prepared using self-referencing dyes from the seminaphthorhodamine family (SNARF). The ratio of the emission from the acid and base tautomers of these dyes is insensitive to photobleaching and variations in the excitation intensity. The photophysics of the dyes has been determined. At high concentrations formation of nonfluorescent aggregates of the dyes results in reduced emission yields. The fluorescent lifetimes of the dyes are unaffected by concentration. The pK(sub a) of the dye-polymer composite is sensitive to the structure of the polymer. This sensitivity is attributed to a difference in energy of the conjugate base of the dye as a function of the amount of cross-linking of the polymer. The pH sensors show mpH response in the physiological pH range (6.8-7.8) and fast hydration and response times. The CO2 sensors show 1-2 Torr response with partial pressures of CO2 in the range of 10-100 Torr and have response and hydration times on the order of several minutes.