Fumigation of the 15th century roof of King's College Chapel, Cambridge, UK, was performed annually fr om 1963-75, with an application rate of 95 mg gamma-HCH + 197 mg dieldrin per m³. The annual emergence of beetles declined from over 1300 prior to 1963 to under 100 from 1973 onwards. The long period required to achieve control is related to the long and variable period which the larvae spend in the wood, unaffected by surface deposits, until their emergence as adults. The total cost of the 13 annual treatments was about pound sterling 280.