Zinc, copper and cadmium accumulation was measured in two herbivorous gastropod molluscs Austrocochlea constricta and Bembicium auratum from Lake Macquarie NSW an area with a history of trace metal pollution. The investigation consisted of three main parts. The first part examined the influence of organism mass and location within the Lake on whole body tissue metal concentrations. This part of the study also compared the distributions of tissue metal concentrations of populations from Lake Macquarie, a known polluted environment, with those of populations from Jervis Bay NSW, an unpolluted environment, to establish whether either species is a net accumulator of zinc copper or cadmium. The second part of the investigation examined a range of factors which may influence whole body metal concentrations. One location in Lake Macquarie was sampled monthly from August 1995 to July 1996. The factors examined were temporal variation, gender, breeding cycle, and tissue distribution. The final part of the investigation examined the detoxification and storage of excess metals in the gastropods from Lake Macquarie. The mechanisms studied were metallothioneins and granules. The tissue metal concentrations of both species were found to be independent of mass. Location within Lake Macquarie did not significantly influence tissue metal concentrations. Variation between individuals was the most significant contribution to overall variation, resulting in a positive skewing of sample trace metal distributions. B. auratum populations from Lake Macquarie had significantly higher copper and cadmium tissue concentrations and A. constricta populations had significantly higher zinc, copper and cadmium tissue concentrations than the populations from Jervis Bay. This suggests that regulation of these metals is not occurring. A. constricta may therefore be considered a net accumulator of zinc, copper and cadmium and B. auratum of copper and cadmium. Tissue metal concentrations did not vary significantly over time. It is suggested that the organisms are in equilibrium with their environment. B. auratum has higher natural equilibrium concentrations than A. constricta particularly for copper and cadmium, suggesting different routes of exposure, uptake or accumulation for the two species. Gender and breeding cycle did not significantly influence tissue metal concentrations. Most of the variability in total copper and cadmium concentrations of both species was explained by variability in gonad tissue metal concentration, while variability in the gonad and somatic tissues zinc concentration explained about an equal amount of the variability in total zinc concentration. A. constricta and B. auratum were both found to induce a cadmium binding protein which has some features in common with metallothionein. A protein of around 10 000 Da which binds approximately 60% of the soluble cadmium was isolated using gel filtration. This protein was further separated into two isoforms using anion exchange. The first isoform eluted at the same time as MT I and the second at the same time as MT II rabbit liver standard. Large cells containing granular material which stained positive for calcium were observed interspersed among the connective tissue immediately behind the columnar epithelial cells lining the gut wall in both species under a light microscope. Calcium positive granular particles were also observed within the columnar epithelial cells of B. auratum. These species have been shown to be net accumulators of the trace metals investigated, with the exception of zinc in B. auratum. It has also been established that organism mass, gender and reproductive state, the partitioning of metals between tissues, and temporal effects are not confounding factors for the purposes of comparing trace metal concentrations between populations. They should therefore be effective biomonitors of the trace metals investigated, with the exception of zinc in B. auratum.