An earlier study of metals in the polychaete Owenia fusiformis showed that individuals within intertidal populations were remarkably variable in terms of whole-body concentrations of zinc and copper. Four populations have now been studied, two in south Cornwall (Fal Estuary and Par Sands) and one each in east Devon (Torre Abbey Sands) and north Brittany (Grève de St Michel). Investigations of the distributions of zinc and copper within the body have demonstrated that consistently zinc is concentrated in the middle body whilst copper increases to a maximum posteriorly. Zinc is accumulated in the mid-gut cells in the form of numerous spherules, 1–2 μm in diameter: X-ray microanalysis shows these to be largely composed of zinc phosphate but containing also magnesium, calcium and iron, together with sulphur and chlorine. Viewed under the microscope the spherules are greenish due to a pigment identified by high performance liquid chromatography absorption scanning as a pheophorbide-like chlorophyll-degradation product. In contrast, copper is widely distributed throughout the body and much is deposited as small granules, 0.2–0.3 μm in diameter, in laminar groupings in hypodermal and peri-intestinal tissues. The identity of the green pigment responsible for the characteristic body colour of O. fusiformis has not been specifically determined but it appears to have a copper basis since dark-green tissues have a significantly higher copper content than those with a light-green colour. The possible role of chlorophyll degradation products in zinc and copper uptake is discussed.