Forward masked thresholds for a 1000-Hz tone were measured for 3-month-old infants and for adults. The masker was a broadband noise burst, 100 ms in duration. Masker level was either 65 or 75 dB SPL. The tone had 16-ms rise, 16-ms fall, and no steady state duration. Masked thresholds were measured at Δt of 5, 10, 25, and 200 ms. The Observer-based Psychoacoustic Procedure [Olsho et al., Devel. Psychol. 23, 627–640 (1987)], was used to estimate infant thresholds. Compared to published data from adult listeners, 3-month-olds appear to show relatively more masking at short Δt. In addition, infants may exhibit masking at very long values of Δt, suggesting an additional nonsensory source of masking under certain conditions. Finally, the effects of increasing masker level on the amount of masking seen in infants will be examined. [Work supported by DC00396 to L. A. Werner.]