We studied the dynamics of intramolecular proton transfer in the glycolate anion, and of the analogous processes in the deuterated and tritiated derivatives, by means of variational transition state theory with various multidimensional semiclassical models of tunneling. Rate constants were obtained directly from MP2/6-31++G** ab initio results scaled so that the height of the barrier coincided with the value given by QCISD/6-31++G** calculations, 3.81 kcal/mol. In this kind of system, the effective barrier height can be significantly lower for the lighter isotope. Analysis of the kinetic isotope effects (k(H)/k(D) and k(H)/k(T)) showed them reduced by tunneling but favored by certain vibrational modes.