Bilateral amplification seems to be the best solution for bilaterally hearing-impaired persons. Nevertheless, some individuals are unsuccessful with this strategy. The goals of the present study were to develop tests to improve the diagnostic test battery before rehabilitation of hearing-impaired persons with bilateral or unilateral amplification, and to evaluate the tests with normally-hearing subjects and with two groups of hearing-impaired persons. The latter two groups contained 11 successful and 11 unsuccessful users of bilateral amplification respectively. Hearing thresholds, speech recognition in noise, signal analysis ability, binaural abilities, and dichotic tests were used in the investigation. The subjects answered a questionnaire and hearing aid gain curves were measured. The results for the two groups were similar for peripheral hearing functions and binaural performance. The unilateral amplification group showed significantly worse results in speech-in-noise and dichotic tests. Spatial aspects within the questionnaire were correlated to amplification preference. We therefore suggest the inclusion of speech-in-noise, dichotic tests, and questions on spatial orientation into the diagnostic scheme before rehabilitation with hearing aids.