The discomfort caused by the noise and vibration in cars is investigated in this thesis to improve understanding of how subjective judgements of noise and vibration affect each other, how the relative discomfort of noise and vibration depend on their magnitudes and their durations, and how the total discomfort caused by simultaneous noise and vibration can be predicted. Two experiments were designed to determine the magnitude-dependence of the relative discomfort caused by noise and vertical whole-body vibration. Subjects were presented with various combinations of different levels of noise and different magnitudes of vibration, and rated the discomfort caused by noise relative to the discomfort caused by vibration, and also vibration discomfort relative to noise discomfort. The subjective equivalence between noise and vibration was highly dependent on whether noise was judged relative to the vibration or vibration was judged relative to the noise. When judging noise, higher magnitude vibrations appeared to mask the discomfort caused by low levels of noise. When judging vibration, higher level noises appeared to mask the discomfort caused by low magnitudes of vibration. The duration-dependence of the relative discomfort of noise and vibration was then investigated. Subjects were presented with 49 combinations of seven levels of noise and seven magnitudes of vertical whole-body vibration, and with five durations (2, 4, 8, 16, and 32 s). Either the discomfort caused by noise relative to the discomfort caused by vibration, or vibration discomfort relative to noise discomfort were rated in two sessions. The findings indicate that noise discomfort and vibration discomfort have a similar dependence on duration. The slopes expressing the levels of noise (sound pressure level or sound exposure level) judged equivalent to the levels of vibration (logarithms of the r.m.s. acceleration or vibration dose value) increased with increasing duration when judging noise relative to vibration, but were independent of duration when judging vibration relative to noise. As the durations increased from 2 to 32 s, the masking effect of vibration on noise discomfort decreased, whereas the masking effect of noise on vibration discomfort did not change. Finally the noise discomfort in the presence of vibration, vibration discomfort in the presence noise, and the combined discomfort of simultaneous noise and vibration were investigated by employing the method of absolute magnitude estimation. Subjects judged noise discomfort, vibration discomfort, and their total discomfort in different sessions. The results suggest that, within the range of stimuli magnitudes investigated, the discomfort caused by vibration was reduced by noise whereas the judgement of noise discomfort was not significantly influenced by vibration. The total discomfort caused by simultaneous noise and vibration was well predicted by ψc = [(ψv)2+ (ψs)2]0.5, where ψv, ψs, and ψc, represent vibration discomfort, noise discomfort, and their total discomfort, respectively. In conclusion, the relative discomfort caused by noise and vibration varies according to whether subjects are asked to judge noise discomfort relative to vibration discomfort or vibration discomfort relative to noise discomfort. There are masking effects of noise on the judgement of vibration discomfort, and of vibration on the judgement of noise discomfort, depending on the relative magnitudes of the two stimuli. The influence of vibration on the judgement of noise discomfort decreases with increasing duration of the stimuli, whereas the influence of noise on the judgement of vibration discomfort is independent of the duration. The discomfort caused by a combination of noise and vibration can be predicted by root-sums-of-squares of the discomfort caused by noise and the discomfort caused by vibration when these stimuli are presented alone.