To investigate the effects of a lateral G force, eight stress panel members were each subjected to a series of stresses using +/- 1.5, 2, or 2.5 Gy combined with either +/- 1 or +/- 2 Gz, for 30 s followed by a 60-s recovery period. Peripheral arterial oxygen saturation, utilizing a Hewlett-Packard 47201A ear oximeter and heart rate were recorded. A consistent fall in arterial oxygen saturation (SaO2) was observed during all the Gy/Gz exposures with the +Gy direction giving the lowest value of 90.1% SaO2 (PaO2 of less than 60 mmHg). A small but consistent increase in heart rate (HR) was also observed during, and for 15 to 20 s after the Gy/Gz exposure. These results indicate that the cardiopulmonary system is stressed during combined Gy/Gz acceleration and the most important change occurs in SaO2.