Nineteen Navy volunteers were exposed, for periods up to 48 hours, to simulated motion environments predicted for a 2,000,000 Kg 2200 ton surface effect ship. Surface effect ships, which are supported by a cushion of air, operate at high speeds and produce motion strongly influenced by the dynamics of the air cushion. The motions of both the environment and the head of each volunteer were measured during scheduled 5 minute intervals and the relationship of head motion to impending emesis was investigated. The time series data and the frequency spectra were examined to identify variability in head response resulting from repetitions with the same subject, repetitions with different subjects, repetitions with a subject in different positions, repetitions simulating different ship operating conditions, repetitions with and without pitch and roll motions, differences between well and sick subjects, fatigue, and progression to emesis. Heave, pitch and roll motions in the range of 0.05 to .5 Hz were simulated. Results of the analysis indicated that a correlation between spontaneous head motion and motion sickness exists. Additionally, the results demonstrate the utility of studying the effects of motion in a controlled laboratory environment. The methodologies developed may readily be extended to other ship motion problems.