Abstract: Rate constants for the reaction of (haloalkyl)-l, 5-diazabicyclo [3.3. O] octadienediones (halo-9, lO-dioxabimanes) with the tripeptide thiol, glutathione (GSH), are reported. Certain bromobimanes are fluorescent labeling agents for thiols. Monohalobimanes and glutathione react by either displacement or reduction (replacement of alkylhalogen by hydrogen). Dihalobimanes react with glutathione in two stages:(1) ...