Fluorescence resonance energy transfer (FRET) is widely used in spectral codification of information at the molecular level, and can be used to generate several layers of information on a DNA chip. We used two oligonucleotides (probes) labeled with different donor (harvesting) molecules in hybridization experiments with complementary oligonucleotides labeled with four different acceptors (targets). By looking at the fluorescence response of the sample after "specific" excitation of each donor molecule (by "specific" we mean a wavelength where one of the donors is predominantly excited), we inspected the possibility t o identify the complementary oligonucleotide hybridized to the probe, in mixtures containing two donor probe/acceptor target pairs. In most samples (13 out of the 16 possible), it is trivial to identify the complementary target that is hybridized to the excited donor probe in the mixtures. The major limitations of the chosen system arise when very different concentrations of donor probe/acceptor target pairs are present in the same sample. (C) 2008 Elsevier B.V. All rights reserved.