The identity of the wave messenger mediating the propagation of intracellular Ca2+ waves in a variety of cells is currently controversial. There is disagreement as to whether the observed waves are mediated by the diffusion of Ca2+ or by the diffusion of inositol 1,4,5-trisphosphate. Resolution of this question will help to elucidate the mechanisms underlying intracellular Ca2+ waves and oscillations. It has been suggested that the diffusion coefficient of the wave messenger, D, may be evaluated by means of the profile equation, D = cλ, where c is the wave speed, and λ is the space constant of the wave front. We show that this equation is not, in general, correct. We derive a more comprehensive form of the profile equation, including the effect of buffering of the wave messenger, and show that the profile equation may be used to estimate the diffusion coefficient of the wave messenger only if the details of the reaction and buffering kinetics are known.