Vibrotactile signals were presented to S’s index fingertip during a specified observation interval at a signal probability of either .30 or .70. The S’s task was to report the presence or absence of the signal as quickly as possible and to estimate the magnitude of the sensory event experienced during the observation interval. Measures of detection probability, reaction time, and sensation magnitude were found to be a function of signal intensity only for vibration amplitudes greater than 1 micron. This finding, coupled with the finding of bimodality in the frequency distributions of the sensation magnitude judgments for the no-signal trials, suggested the operation of absolute thresholds in vibrotactile signal detection.