Because man lacks the ability to alter the earth’s gravitational field, concepts of its effects on organisms have been derived indirectly. Classically, the biological effects of gravity have been inferred from differences observed between different sized animals, since the influence of gravity upon a system is generally dependent upon its size. 1 More recently, information has been added from procedures which limit the effectiveness of gravity, e.g., water immersion and chronic recumbency. Particularly important is information, only now becoming available, on animals removed from gravitational influence in Earth-orbital weightlessness. Observations in augmented gravity fields, produced by protracted centrifugation, also are useful in resolving gravitational effects. The kinetics of acceleration relationships can be estimated with findings from animal exposures to several field strengths.