A series of experiments investigated practice effects on 1.25-dB SISI scores with three groups of normal-hearing subjects. All tests were administered at 20-dB SL. The experiments investigated the effects of practice, performance retention, frequency, and feedback. SISI scores increased with practice, and increased SISI scores persisted after three weeks of no practice. Increased SISI scores were not a function of frequency; however, the rate of increase tended to be greater for 4000 Hz than for 1000 Hz. Results indicated that increased SISI scores may be enhanced by, but are not dependent upon, feedback. In summary, SISI scores are subject to practice effects.