Measurements of the way the oculomotor system adapts to prism-induced heterophorias have been made in eight normal subjects. Adaptation to 2 delta vertically and, on separate occasions, to 6 delta horizontally was found to be substantially completed after only 2-3 minutes of binocular visual experience. The form of the adaptive process for distant targets was asymmetrical in the horizontal meridian, being faster after the insertion of 6 delta base-out than for 6 delta base-in. This asymmetry largely disappeared for near vision.