The effectiveness of lethal rabbit management techniques is reduced by surviving or immigrating rabbits having continued access to the burrows. This study will aim to increase the long-term cost-effectiveness of control by identifying methods of destroying burrow systems after rabbits within the systems have been removed. The study will be composed of 2 specific objectives outlined as follows, together with ways in which they might be achieved: 1. Development of a technique to block rabbit burrows. The feasibility of putting PFA into bags will be assessed, after which a small scale field trial will be performed to examine the ease with which empty burrows can be blocked with PFA in sacks or without sacks. Some burrows will be excavated to determine the extent of blocking and, if blocking is successful, empty burrows in rabbit-proof pens will be blocked using soil, PFA in sacks or PFA without sacks. Known numbers of rabbits will be placed in these pens for approx. 1 month to determine whether they can dig out the PFA; and 2. Validation of the technique in the field. 4 sites each will receive 1 of 2 treatments, removal of rabbits from the warrens and blocking with soil (normal rabbit control), or removal and blocking with PFA. Prior to treatment, the extent of warrens, the location and interconnections between burrows, and the abundance of each rabbit population will be surveyed. A number of rabbits at each site will be fitted with radio transmitters and released, and their positions in the warrens will be determined before removal. After removal, all burrows will be blocked with soil initially and any burrows reopened within a few days will be retreated. Population growth will be monitored. Any reopened or new burrows will be noted and retreatment will be considered where appropriate. In this way, the cost-effectiveness of the 2 methods will be compared. Results will be disseminated to those involved in organising and conducting rabbit control or with responsibilities for rabbit control.