A three-dimensional pressure-sphere anemometer and fast thermometer system (P.S.A.T.) was used to measure vertical heat flux density in the atmospheric surface layer at 1–4 m above alta fescue and snap beans. Good agreement with independent measurements was obtained, which shows the the P.S.A.T. is sufficiently small and has adequate high-frequency response and accuracy for eddy correlation measurements within 1 m of the surface. Also obtained with the P.S.A.T. were (u′T′)/(w′T′), ru,T, rw,T and σT/T*, and their dependence upon stability. When the atmosphere was thermally stable, slow wave motions frequently increased σT even though turbulent mixing was lacking. Abstract A three-dimensional pressure-sphere anemometer and fast thermometer system (P.S.A.T.) was used to measure vertical heat flux density in the atmospheric surface layer at 1–4 m above alta fescue and snap beans. Good agreement with independent measurements was obtained, which shows the the P.S.A.T. is sufficiently small and has adequate high-frequency response and accuracy for eddy correlation measurements within 1 m of the surface. Also obtained with the P.S.A.T. were (u′T′)/(w′T′), ru,T, rw,T and σT/T*, and their dependence upon stability. When the atmosphere was thermally stable, slow wave motions frequently increased σT even though turbulent mixing was lacking.