Commercially available fish oil supplements sourced from retail outlets in the UK, as well as by mail order, were surveyed in 2000-02 for dioxin (PCDD/Fs) and polychlorinated biphenyl (PCB) content. Sampled products were representative of market share. The WHO-TEQ values for these products ranged from 0.18 to 8.4 ng kg-1 for SigmaPCDD/F and from 1.1 to 41 ng kg-1 for Sigma dioxin-like PCBs. The results suggest a downward trend in the levels of dioxins in fish oil supplements over the last decade, since levels for similar products ranged from 0.3 to 10 ng kg-1 for SigmaPCDD/F WHO-TEQ in 1996. Levels of ICES (International Council for the Exploration of the Seas) 7 PCBs in the current study ranged from 8.3 to 267 microg kg-1. Subsequent to this survey, European Union legislation has been introduced that includes a maximum limit of 2 ng kg-1 WHO-TEQ for dioxins in fish oil products for human consumption. Twelve of the 33 products reported here would have exceeded this limit. Negotiations are in progress to incorporate dioxin-like PCBs into the European Union regulations. When manufacturer-recommended doses were applied to the observed levels, the estimated upper bound human exposure to dioxins and dioxin-like PCBs from dietary intake of these products ranged from 0.02 to 7.1 pg WHO-TEQ kg-1 body weight day-1 for adults and from 0.02 to 10 pg WHO-TEQ kg-1 body weight day-1 for schoolchildren. This level rises to 1.8-8.9 pg WHO-TEQ kg-1 body weight day-1 for adults and 1.4-14 pg WHO-TEQ kg-1 body weight day-1 for schoolchildren when combined with the average exposure from the whole diet in 1997. Again, subsequent to this survey, the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) revised the UK tolerable daily intake (TDI) for mixtures of dioxins and dioxin-like PCBs from 10 to 2 pg WHO-TEQ kg-1 body weight day-1. This is in line with the tolerable weekly intake (TWI) of 14 pg WHO-TEQ kg-1 body weight set by the Scientific Committee on Food (SCF).