We report observations of the ionization of atomic potassium by simultaneous absorption of three dye laser quanta. The laser wavelength is tuned through the two‐photon resonances with the 6S1/2and 4D3/2,5/2states, and the dependence of the ionization probability on the laser wavelength is investigated for linearly and circularly polarized light. Our results are in agreement with the selection rules and theoretical estimates of the ionization probability.