A new technique is proposed to infer the parameters in a generalized three-parameter gamma function model for the distribution of drop sizes in rain, from measurements of rainfall rate and path attenuation through the rain at infrared wavelengths, where raindrop cross sections are essentially independent of frequency, and comparison with simultaneously measured rain attenuations in the millimetric wavebands. The technique is shown to be single-valued and stable, for a particular form of the gamma function. The resultant drop size distributions have been used to calculate millimeter-wave rain attenuations which are in excellent agreement with those measured. ¿ American Geophysical Union 1995