The potential of different mathematical methods for the recovery of reactivity distributions, f(k), from steady-state isotopic transient kinetic analysis (SSITKA) data has been tested and compared using a model catalyst system that consisted of a mechanical mixture of two catalysts with catalytic sites of known and different reactivity. Fitting one or two exponential functions to the measured transients confirmed the presence of two different pools of reaction intermediates, but the use of this method for determination of f(k) is limited to simple catalytic systems. For more complicated systems, the Tikhonov/Fredholm method might be superior to the inverse Laplace transform method.