The reaction of the glutathiyl radical (GS(center dot)) with a widely used spin trap N-tert-butyl-alpha-phenyinitrone (PBN) has been studied in the presence of various methylated P-cyclodextrins and with PBN covalently bound to dimethylated beta-cyclodextrin (PBN-DIMEB) and permethylated beta-cyclodextrin (PBN-TRIMEB). Scavenging rate constants for GS(center dot) by PBN were obtained in the presence of randomly methylated cyclodextrin (RAMEB) and PBN-TRIMEB and found to be close to the rate constant previously measured for PBN. RAMEB and 2,6-di-O-Me-beta-cyclodextrin (DIMEB) were found to be the most efficient in the increasing PBN/GS(center dot) lifetime, by a factor of 5.5 for RAMEB and 6.8 for DIMEB compared with the lifetime of PBN/GS(center dot). It is concluded that the presence or "attachment of" beta-cyclodextrins does not influence the scavenging rate constant of GS(center dot) but it does lead to stabilization of the spin adducts formed.