Traditional methods of vertebrate pest control, notably lethal control techniques, are often of limited effectiveness, are environmentally hazardous and are increasingly socially unacceptable. The aim of this study will be to examine the potential of semiochemicals (social and predator odours) to limit the growth of vertebrate pest populations, by disrupting social organisation and sexual activity. House mice (Mus domesticus) and field voles (Microtus agrestis) will be used as model systems as they are cost-effective and differ in important aspects of their social and foraging behaviours and life-history traits. Similarities and differences in responses of mice and voles to semiochemicals will allow identification of the prospects and limits of generalisation of the findings to other vertebrate species, such as rabbits and grey squirrels. The study will be composed of 2 specific objectives outlined as follows, together with ways in which they might be achieved: 1. Quantification of the effect of at least one predator- and one social-semiochemical on physiological and reproductive fitness of individual and paired house mice and field voles. Semiochemicals from predators (e.g. trimethyl-thiazoline from foxes and propyl-dithiolane and propyl-thietane from stoats) and social semiochemicals (e.g. and farnesene from mice and 2,3,5-trimethylpyrazine from voles) will be tested under a range of conditions by gross manipulation of the environment (e.g. changing the amount of cover and light). Assessments will be made of behaviour (resource use, foraging behaviour and territorial marking), indicators of treatment-induced stress (behavioural and biochemical indices) and reproductive physiology (sexual activity, fertility, litter size, litter sex ratios)and 2. Determination of the potential of semiochemicals to limit growth rate of at least 5 colonies of house mice and field voles, by quantifying their effect on colony structure and dynamics. Large scale arena trials will be conducted to determine the response of colonies to semiochemical treatment in terms of social behaviour, reproductive behaviour, productivity and colony growth rate. Initially, paired animals will be introduced into arenas treated with semiochemicals to investigate whether semiochemical can inhibit development of wild colonies. Subsequently, conditions that allow maximum colony disruption by semiochemicals will be determined, both by applying the chemicals at set stages in the colony’s lifecycle, and by studying the optimal siting and density of odour sources that will significantly cut the carrying capacity of the territory. A report will be prepared that summarises the results of this study and evaluates the potential of semiochemicals as pest population management tools. This study offers the prospect of reducing economic and social impacts of vertebrate pests without recourse to lethal control.