An analytical protocol is described for the determination of the toxicologically important PCB congeners 77, 126 and 169 in a wide variety of matrices including human milk and adipose tissue, avian tissue, soil and sewage sludge. Utilising similar containment-enrichment, isotope-dilution principles to those employed in PCDD/F analysis, the method employs liquid chromatography on a Florisiltm microcolumn to separate PCDD/Fs and PCB congeners 77, 126 and 169 from the majority of o-substituted PCBs prior to GC-MS determination. The method is compatible with the analysis of such matrices for PCDDs and PCDFs.