Transient chromatic adaptation produced by an abrupt change of background color permits an easier and closer approach to cone isolation than does steady-state adaptation. Using this technique, we measured middle-wave-sensitive (M)-cone spectral sensitivities in 11 normals and 2 protanopes and long-wavelength-sensitive (L-) cone spectral sensitivities in 12 normals and 4 deuteranopes. Although there is great individual variation in the adapting intensity required for effective isolation, there is little variation in the shape of the M- and L-cone spectral-sensitivity functions across subjects. At middle and long wavelengths, our mean spectral sensitivities agree extremely well with dichromatic spectral sensitivities and with the M- and L-cone fundamentals of Smith and Pokorny [Vision Res. 15, 161 (1975)] and of Vos and Walraven [Vision Res. 11, 799 (1971)], both of which are based on the CIE (Judd-revised) 2 degrees color-matching functions (CMF's). But the agreement with the M-cone fundamentals of Estévez [Ph.D. dissertation, Amsterdam University (1979)] and of Vos et al. [Vision Res. 30, 936 (1990)], which are based on the Stiles-Burch 2 degrees CMF's, is poor. Using our spectral-sensitivity data, tritanopic color-matching data, and Stile's pi 3, we derive new sets of cone fundamentals. The consistency of the proposed fundamentals based on either the Stiles-Burch 2 degrees CMF's or the CIE 10 degrees large-field CMF's with each other, with protanopic and deuteranopic spectral sensitivities, with tritanopic color-matching data, and with short-wavelength-sensitive (S-) cone spectral-sensitivity data suggests that they are to be preferred over fundamentals based on the CIE 2 degrees CMF's.