A new formulation of quantum transition state theory for adiabatic reactions is proposed. It is based on the flux-flux correlation function of Miller, Schwartz, and Tromp, and calculation of a rate constant requires only the calculation of this correlation function and its second derivative at zero time. The theory is tested for a one-dimensional Eckart barrier and a parabolic barrier linearly coupled to a harmonic oscillator. This quantum transition state theory is exact for a one-dimensional parabolic barrier, is accurate for the model problems studied even under highly quantum conditions, and in the classical limit (($) over bar h-->0) becomes classical transition state theory. An analytic continuation procedure for calculating corrections to the transition state theory is discussed.