The ecology of the sand lizard (Lacorta agilis) and the sympatric common lizard (Lacorta vivipara) was studied at two sites in Dorset, England from 1975 to 1977. Lizards wore caught in dry pitfall traps at one site and by hand at the other. Each individual caught was weighed, measured, and marked, before release. Diet was studied by faecal analysis. Both species took invertebrate pray of a variety of types and sizes but there were several taxonomic differences in prey taken. L. gilis took larger and border prcy than L. vivipara. Relationships between prey length and snout-vent length were examined for both species. Prey of L. agilis in spring was smaller, harder, and less diverse than in summer. Food consumption, measured by production of nitrogenous excreta, was lower in spring. Factors affecting production of nitrogenous and faecal excreta were investigated. Faecal excreta was unsuitable as a measure of food consumption for L. agilis because of its relationship with prey hardness. Stomach capacity of L. agilis was much greater than normal daily levels of food consumption. Individuals appeared capable of exploiting locally and seasonally abundant prey by feeding at high rates. Reproductive effort of L. agilis increased with age. Annual adult mortality was estimated as 28%. Densities at both sites wore approximately 50 individuals hectare 1. Sub-adult L. amilis grow faster than sub-adult L. vivipara 3~horgy devoted to growth by different ago classes of both species is compared. Individuals of L. agilis had overlapping home ranges and did not defend territories. It is suggested that home range size is too large to allow resources to be defended. Pitfall traps caught 7 times more L. agilis than L. ivipara. Rates of capture of L. agilis increased with increasing temperature and radiation whereas those of L.vivipara did not.