We have studied the simultaneous complexation of pyrene and perylene with gamma-cyclodextrin in water by means of electronic excitation energy transfer. We found evidence that although in the solution there are present three different pyrene/gamma-cyclodextrin complexes with stoichiometries of 1:1, 1:2, and 2:2 the (perylene)(1)/(gamma-cyclodextrin)(2) complex that is formed associates exclusively with the excimer-emitting (pyrene)(2)/(gamma-cyclodextrin)(2) adduct and not at all with the others. Moreover, this effect is not observed when pyrene is replaced by some of its homologues, which also form 2:2 excimer-emitting complexes with gamma-cyclodextrin.