1. A food store infested with house-mice (Mus musculus L.) was treated with boxes containing 1% warfarin dust surrounding a solution containing 0·005% sodium warfarin and 5% sugar. The boxes were placed around the bases of the stacks, in the air-lanes between stacks and at eaves height at the gable ends of the store.

2. Census baitings with counted numbers of wheat grains showed that the mouse population was reduced by about 95% after 5 weeks of the poison treatment and by almost 100% after 20 weeks.

3. The field trial suggests that the combined use of rodenticidal dust and poison solution baiting points is a useful additional method of controlling M. musculus and is most effectively employed against mice living in warm, dry environments.

Thanks are expressed to our colleague Mr E. W. Powell, who co-operated in this work.