Donor and acceptor spheres are generated by the Monte-Carlo technique, and then donor fluorescence intensity decay profiles were created by the direct energy transfer method. The donor intensity curves were simulated by convolving them with the experimental lamp profile and Gaussian noise was added to create realistic decay profiles for the time-resolved fluorescence (TRF) experiments. Donor intensity decays were fitted to the phenomelogical equation to obtain the decay parameters to test the reliability of TRF experiments at several interdiffusion steps of donor and acceptor spheres. The simulations show that fit procedures which attempt to obtain all parameters simultaneously are not reliable. The interaction parameters must be obtained using the data obtained at complete mixing. This parameter must then be held constant while the diffusion parameters are sought. (C) 1998 Elsevier Science Ltd. All rights reserved.