Studies of tissue metal concentrations in shellfish have progressed along two major lines: first, to record the range of concentrations within commercial species, a response to the need to identify potentially hazardous levels from a human nutritional standpoint; and second, to compare concentrations within a single species on a geographical basis as a framework for an environmental monitoring programme. Body size is a parameter which can influence tissue metal concentrations, and if significant variations due to size do occur, then clearly it is a factor which should be taken into consideration within these contexts.