Fifty-three healthy US Air Force aircrewmen, 26-55 yr old, volunteered for a centrifuge study designed to determine the effect of age on relaxed +GZ tolerance. Each was subjected to G forces of gradual and rapid onset, with G tolerance determined by standardized contraction of peripheral visual fields. Of the subject characteristics studied, only age was positively correlated with rapid-onset G tolerance; both age and weight were positively correlated with gradual-onset G tolerance. A combination of age and weight gave a stronger positive correlation with G tolerance (rapid- and gradual-onset) than did either characteristic alone. No significant negative correlations were observed. We conclude that aging may offer some protection from G stress; there is no evidence that aging leads to a decrement in G tolerance.