In the production of plug seedlings, the air current speed around the seedlings is an important environmental factor affecting the rates of net photosynthesis (P) and evapotranspiration (E) . In the present experiment, a plug sheet consisting of tomato plug seedlings and soil mix was placed in a wind tunnel with artificial lights, and the P and E rates of the plug sheet were examined under different air current speeds, at an air temperature of 29-30°C, relative humidity of 60-70%, CO₂ concentration of 340-360 μmol mol^-1 and photosynthetic photon flux density of 270 μmol m^-2s^-1 At the inlet and outlet of the wind tunnel, absolute humidities (y_in and y_out, respectively) and CO₂ concentrations (C_in and C_out, respectively) were determined with a dew point analyzer and an infrared CO₂ analyzer, respectively. The weight of the plug sheet was measured with an electronic balance. The E was estimated based on the change with time in the weight of plug sheet. The air flow rate in the wind tunnel, F, was determined using an equation : E = F (y_out-y_in) /A, where A is the area of plug sheet. The P was determined using the equation : P=F (C_in - C_out) /A. The P and E increased as the air current speed and LA! (leaf area index of the seedlings) increased. However, the increase in P with the increase in LAI was less than the increase in E with the increase in LAI. Eleven days after seeding, when LAI=0.43, the P and E at an air current speed of 0.6 m s^-1 were 1.4 and 1.9 times those at an air current of 0.1 m s^-1, respectively.