To test the prophylactic value of anti-motion sickness drugs, a randomized double-blind trial was undertaken on 46 young, healthy, male volunteer marines. Comparison was made between a transdermal therapeutic system (TTS) containing as the effective agent scopolamine (TTS-scopolamine) and proprietary meclozine tablets. An artificial "sea voyage" served to produce motion sickness, each subject sitting by himself on an artificially tilting "island", on two days for 30 minutes. Without treatment, 19 of the 46 subjects developed symptoms of motion sickness requiring treatment. After administration of TTS-scopolamine or meclozine tablets (double-dummy technique) the motion sickness score was reduced by 89% and 59%, respectively. There was a reduction on the visual analog scale of 98% and 59%, respectively. Probability of error (Fisher's exact probability test) for assuming therapeutic advantage of TTS-scopolamine over meclozine tablets was 13.5%. A pre-set significance level of 5% was thus not reached. This trial shows that TTS-scopolamine, even in a brief exposure, has at least the same effectiveness as meclozine, in addition to avoiding the gastrointestinal tract and maintaining with certainty a constant blood level over three days.