The antagonistic effects of unfolding of a protein (lysozyme) by urea and refolding by sodium dodecyl sulfate (SDS), have been studied by solvation dynamics and circular dichroism. Efficient fluorescence resonance energy transfer from tryptophan to coumarin 153 (C153) indicates that the solvation probe, C153 is located near tryptophan 62 and 108 of lysozyme. The average solvation time of C153 bound to lysozyme in 7 M urea and 3 mM SDS is quite close to that in the native state of lysozyme while in 28 mM SDS and 7 M urea the average solvation time is nearly three times slower. (C) 2004 Elsevier B.V. All rights reserved.