The differential equation governing the temporal variation of the distribution density, φ(X, t), of D-A transfer rates has been derived directly from the macroscopic differential equations of energy transfer for the cases where the covariance coefficient of D-A transfer rate, X, and D-D transfer rate, W, equals 0 or 1. φ(X, t) may be expressed as a function of φ0(X), the static distribution density of D-A transfer rates, and F(t), the decay dynamics of the donor flourescence. F(t) derived by normalizing φ(X, t) coincides with the results of Burshtein's hopping model. © 1990.