Background: Low frequency translational oscillation can provoke motion sickness in land vehicles, ships and aircraft. Although controlled motion experiments indicate a progressive increase in nauseogenicity as frequency decreases toward 0.2 Hz, few data are available on the existence of a definite maximum nauseogenic potential of motion around 0.2 Hz, or decreased nauseogenicity below this frequency. Hypothesis: Nauseogenicity should be maximal around 0.2 Hz. Methods: We selected 12 subjects for high motion sickness susceptibility, and they were exposed to horizontal sinusoidal motion (1.0 m.s-2 peak acceleration) at 3 different frequencies (0.1, 0.2 and 0.4 Hz), at 1-wk intervals at the same time of day, according to a factorial design. Subjects were seated comfortably in the upright position with head erect. Fore-aft motion was through the body and head X-axis. Motion was stopped (motion endpoint) at moderate nausea or after 30 min. Results: The proportion of subjects experiencing moderate nausea was maximal at the intermediate frequency: 8/12 at 0.1 Hz, 12/12 at 0.2 Hz, 7/12 at 0.4 Hz. The mean time to motion endpoint was significantly (p < 0.01) shorter at the intermediate frequency: 18.0 min at 0.1 Hz; 11.2 min at 0.2 Hz; 20.2 min at 0.4 Hz. Similar frequency patterns emerged for other sickness ratings. The equivalent times to achieve moderate nausea using estimated values to correct for subjects who reached the 30 min time cut-off were: 22.7 min at 0.1 Hz; 11.2 min at 0.2 Hz; 28.1 min at 0.4 Hz. Conclusions: A maximum nauseogenic potential around 0.2 Hz was substantiated.