Differences in response among differentiating tracheids to the stimulus of stem inclination were examined at three heights in stems of young trees of Taxus cuspidata Sieb. et Zucc. A change in the orientation of the helical cell wall thickenings from an S- to a Z-helix with a simultaneous absence of an S3 layer were the first anatomical responses to appear. These changes first occurred in differentiating xylem on the underside of the upper segment of the stem after 4 days inclination. The gravistimulus for compression wood formation was transmitted basipetally within the stem as the tilting period was increased. After 10 days, the xylem on the underside of the upper segment of the stem contained five mature cells with a Z-helix, indicating that deposition of the thickenings required 2 days. The present results suggest that the rate of cambial division and xylem differentiation differs longitudinally in an inclined stem. For Taxus cuspidata, a change in the orientation of the helical thickenings should be a useful marker for deciding whether or not the differentiating cells have perceived the stimulus for compression wood formation.