Suppression tuning curves (STCs) for spontaneous otoacoustic emissions (SOAEs) were longitudinally obtained in seven infants (at 3 weeks, 2 months, and 3, 4, or 6 months of age) and in five adults. Excellent reproducibility was obtained for adult STCs. Reproducibility for infant STCs was poorer, but the curves at each age resemble those of adults both qualitatively and quantitatively as measured by slopes of the lower and upper segments of the STCs and by Q10''s. Evidence from two subjects suggests that developmental changes in the fine tuning of the system may occur postnatally. Results are discussed with respect to the development of cochlear frequency selectivity.