Dyes commonly used as biological labels have been used to probe resonance energy transfer in organized media. In neat water, energy transfer between the dye pairs fluorescein (donor):Nile red (acceptor) and acridine orange (donor):Nile red (acceptor) has a very low probability of occurrence. This study shows that the rate constant of energy transfer increases by more than an order of magnitude in organized surfactant media, viz., micelles and reverse micelles of the surfactant Triton X-100. The reverse micelles provide a better medium for energy transfer than the micelles. The energy transfer studies also provide an idea about the location and proximity of donor and acceptor dyes within the various organized media. Assuming Poissonian statistics for dye distribution, the donor-acceptor distances within micelles and reverse micelles are determined from energy transfer parameters. Acridine orange has been found to function better as a donor than fluorescein. This may be due to steric and electrostatic factors. (C) 2003 Elsevier Inc. All rights reserved.