Just-noticeable differences in bandlimited vertical vibration were studied for subjects sitting on automotive seats. Stimuli consisted of octave band frozen Gaussian noise centered at 4, 8, and 16 Hz. Two-interval forced-choice paired comparisons were used, with a reference level of 8 mg. The level of the alternative stimulus in the pairs varied from 8.25 to 10 mg. Stimulus intensity was measured with a seat pad accelerometer. Stimulus durations of 4 s plus 1/2-s tapers were used for all frequency bands, with 1/2 s between stimuli. Sets of trials with 2-s durations at 16 Hz were done as a test of duration effects. Three subjects were trained with feedback until performance stabilized. Then 200--250 trials were performed in blocks of 25 or 50 for each of four alternatives at each frequency and each subject. Thresholds determined from the psychometric functions ranged from 0.6 to 1.8 mg, with most between 0.6 and 1.2. Little frequency dependence was evidenced over all frequency bands, and little duration effect was seen between 2- and 4-s stimuli at 16 Hz.