Diazepam has been used empirically for the relief of vertigo and, in addition, there are animal studies to suggest that this drug suppresses the vestibular system. One might anticipate therefore that diazepam would be an effective antimotion sickness drug. To study this, motion sickness was generated in four groups of normal subjects by having the subject make controlled head movements while rotating at constant velocity. Every subject was subjected (using a double-blind technique) to four different drug states, namely no drug, placebo, dimenhydrinate, and diazepam. Each group of subjects received the drug state at a different time interval (i.e. 30, 60, 90, and 120 min) prior to the motion sickness exposure. Motion sickness endpoints were measured subjectively using a nausea scale and objectively using a sweat sensor. The results showed significant antimotion sickness properties for both dimenhydrinate and diazepam as compared to the placebo. For the time intervals studied, the maximum effect was obtained at 120 min for both drugs.