A technique is described that allows accurate measurement of input prism coupling efficiencies in single-mode channel waveguides. Coupling efficiencies of >1% were measured. Scattering and absorption losseswere also measured in single-mode channel waveguides and in planar diffused waveguides. All measurements were made in Ti-in-diffused LiNbO(3) waveguides. The channel widths before diffusion were 3 ,microm. Losses for channel waveguides range from 1.34 to 1.66 dB/cm and were measured for both TE and TM modes.