The purpose of this study was to clarify and extend the results of earlier studies of age-related effects on temporal resolution by precisely matching young and old subjects with normal hearing and measuring gap thresholds in a variety of listening conditions. Younger subjects were between 17 and 40 years of age, older subjects between 64 and 77 years. Signals were noisebursts which varied in upper-cutoff frequency, overall level, and sinusoidal-amplitude-modulation depth. Signals were presented in quiet, in a noise floor, and with a gated-high-frequency masker in a noise floor. Significant main effects were found for signal frequency, intensity, modulation, age, and background condition. Mean gap thresholds ranged between 2.1 and 10.1 ms and were larger for the older subjects in all 24 conditions. In some conditions, introduction of a noise floor increased the gap thresholds of the older subjects relative to those of the younger. Analyses of individual data support the conclusion that the mean differences between groups reflect shifts in the distributions of gap thresholds of the older subjects towards poorer temporal resolution.