Detection of a brief (5-msec) sinusoid in the presence of a simultaneous tonal masker was inviatigated. The masker was either a gated sinusoid or a continuous tone. Both signal and gated masker were bandpass filtered. In the continuous-masker condition, when masker frequency was lower than signal frequency, a notch or shelf, similar to that reported by Greenwood [J. Acoust. Soc. Am. 51, 502–543 (1971)] was exhibited. The failure to find a comparable notch for the gated-masker condition suggests that combination tones may not be involved in detection in this condition. When masker frequency was higher than signal frequency, signal threshold in the continuous-masker condition was lower than in the gated-masker condition by as much as 20 dB. This difference in masking between continuous and gated conditions cannot be attributed to the presence of combination tonee; or to energy splatter produced by the gated masker. [This research was supported by an NIH grant.]