The hydrodechlorination of environmental samples of toxic polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), commonly "dioxins", was accomplished catalytically under mild conditions: 50 degreesC and I atm of hydrogen. This catalytic detoxification methodology takes place in a multiphase reaction system (isooctane-water), with a supported metal catalyst (Pt or Pd) modified by a phase-transfer (PT) agent, Aliquat 336. Environmental samples of PCDDs and PCDFs were extracted from the fly ashes of a municipal solid waste incinerator (MSWI), and had a relatively high toxicity equivalent concentration (572 and 735 pgTEQ/ml, respectively). The samples were successfully hydrodechlorinated using the described detoxification methodology, and yielded mixtures where the concentration of contaminants determined by GC-HRMS, was lower than the experimentally detectable limit. The procedure has the potential to become a practical method for the detoxification of PCDDs and PCDFs.