The electroacoustic characteristics of an experimental master hearing aid are determined by the choice of transducers and settings of 26 controls which include a preamplifier, the gains and limiting levels in each of 12 channels as well as the gain of a final power amplifier. Here, a computer program which aids in the fitting of the electroacoustic characteristics of this aid to the characteristics of a patient’s residual hearing is described. The patient’s audiologic data and the hearing-aid parameters are entered into the computer and the gain and limiting level of each channel of the hearing aid are adjusted until an appropriate fit is achieved. The results of the fitting procedure are displayed on a graphics terminal. Permanent copies of the results can be produced on a printer-plotter. Included in the results for each of 12 channels are (1) the discomfort level, most comfortable listening level, and hearing threshold of the patient, and (2) the maximum output and noise floor of the hearing aid as well as the aided speech level. This approach has simplified the problem of fitting a complicated hearing aid to a patient’s residual hearing and seems to offer attractive possibilities for fitting commercial hearing aids in the future.