Nineteen pooled samples of retail cow's milk were analysed for ortho (PCBs 28, 52, 101, 118, 138, 153 and 180) and non-ortho (PCBs 77, 126 and 169) polychlorinated biphenyls. Concentrations of individual congeners in whole milk were in the ranges 2 to 95 ng/kg for ortho substituted PCBs (51 to 2440 ng/kg fat) and 0.05 to 0.6 ng/kg for non-ortho substituted PCBs (1.3 to 15.4 ng/kg fat). These values provide a preliminary estimate of background contamination levels for polychlorinated biphenyls in UK milk. Results expressed in TEQs, using the recently proposed WHO/IPCS TEFs, averaged 0.06 ng TEQ/kg whole milk.