A laser excitation and infrared absorption study of the single C(4v) symmetry centre in KY(3)F(10):Ho(3+) is presented. Comparatively weak upconversion fluorescence is observed and can be attributed to an energy-transfer excitation mechanism proposed previously. Fifty one crystal-field energy levels for seven Ho(3+) multiplets ((5)I(8), (5)I(7), (5)I(6), (5)F(5), (5)S(2), (5)F(4) and (5)F(3)) have been deduced. A crystal-field analysis has been performed, with excellent agreement found between experimental and calculated energy levels.