Contrast thresholds for a 6 c/deg sinewave grating were measured following continuous and interrupted adaptation of 10 min duration to a high-contrast (0.6) sinewave grating of the same spatial frequency. Interrupted adaptation was administered as five 2-min segments, and the interadaptation interval (IAI) was varied from 10 to 180 sec. The results indicate that adaptation to spatial contrast can be described by a two-staged process, each stage having a different time constant of adaptation decay.