Several aspects of the environment of divers should increase their susceptibility to motion sickness: a) sensory conflicts, b) body fluid redistribution, and c) nitrogen narcosis. We tested motion sickness susceptibility by placing subjects on a rotating platform and having them perform stylized heat movements that produced cross-coupled angular accelerations in vestibular end organs until nausea developed. This test was performed once each day on 9 consecutive days while subjects were immersed at the end of 3-4 h of diving. The test was also carried out while subjects were nonimmersed with no preceding diving on the day immediately before and after this 9-day period. Compared with nonimmersed conditions, significantly fewer head movements were required to elicit nausea while immersed (P less than 0.01). We conclude that individuals are more susceptible to motion sickness while immersed in open water than while on dry land.