The variation of fluorescence yield as a function of exciting wavelength for the title compounds has been examined. 1,3,5-Trifluorobenzene shows a maximum in fluorescence yield at an exciting wavelength λex = 2680 Å; for 1,2,3-trifluorobenzene, this maximum occurs near 2740 Å. Triplet yields for both molecules, based on the biacetyl sensitized emission technique, have been determined at various exciting wavelengths. The maximum triplet yield of 1,3,5-trifluorobenzene = 0.40 and occurs at λex = 2640 Å, while that of 1,2,4-trifluorobenzene = 0.64 at λex = 2780 Å. The triplet of the 1,2,4 isomer appears to lie below the triplet ofcis-butene-2 and thus the olefincis–transisomerization technique cannot be used as a diagnostic for the triplet state of this molecule. The effect of two inert gases, cyclohexane andcis-butene-2, on both fluorescence and triplet yield has been studied.