Diurnal changes in stem circumference at the 1954 and 1963 internodes of a 22-year-old Douglas-fir were monitored with automated band dendrometers. Determinations of internal tree water potential and estimates of transpiration were used to characterize the water status of the tree. Environmental monitoring encompassed air temperature along the tree stem and solar radiation above the forest canopy. The 1963 internode, within the live crown, was relatively more sensitive to the factors affecting stem dehydration and shrinkage than the 1954 internode below the live crown. The diurnal patterns of stem shrinkage seemed to be determined by the lag between water absorption and transpirational loss, which was in turn dependent upon soil water supply and atmospheric moisture demand. In addition, transpirational demand appeared to be partially fulfilled by water temporarily stored in stem tissue. Forest Sci. 19:251-255.