Daily transpiration before and after thinning was measured on six individual trees in a 31-year-old Chamaecyparis obtusa Endl. stand by the heat pulse method. After thinning, daily transpiration of a tree at a given level of solar radiation increased, and the difference between before and after thinning increased with solar radiation. The increase after thinning was related to a high rate of crown transpiration caused by greater canopy exposure and, subsequently, to the increase in foliage biomass per tree. Stand transpiration was calculated on the basis of two parameters, daily solar radiation and daily maximum vapor saturation deficit of the air. During the growing season (April to September), transpiration of a tree increased following thinning whereas transpiration of the stand decreased 21% after thinning. This decrease was associated with a 24% decrease in leaf mass of the stand following thinning.