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Blue mussels (Mytilus edulis) taken from several sites in the Mersey Estuary, an urban-industrial water body in NW England, have been analyzed for residues of the persistent organochlorines, DDT, PCB congeners nos. 28, 52, 101, 118, 138, 153 and 180 (ICES7), and α-MHCH (α-methyl hexachlorocyclohexane). The concentration range for ΣPCB (ICES7) was 13.9–34.9 μg kg−1 in 1994 compared with 9.6–31.9 μg kg−1 in 1998, whilst the equivalent concentrations of ΣDDT were 8.9–32.4 μg kg−1 and 4.5–16.8 μg kg−1, respectively. The concentration of α-MHCH, an organochlorine largely restricted to the Mersey Estuary, was 1.2–11 μg kg−1 in 1994 and 0.3–1.3 μg kg−1 in 1998. At both sampling dates the inner estuary sites of Rock Ferry and Egremont were more contaminated than the outer estuary sites of New Brighton, Dove Point and Caldy Blacks. The lower concentrations of organochlorines in mussels in 1998 compared with 1994 are thought to be early evidence of significant improvements in water quality derived from major capital investment in the treatment of industrial effluents and sewage wastewater, linked to a combination of stricter legislative controls and the environmental benefits from the adoption of new, clean technologies in manufacturing.