Colorado beetle is not indigenous to the United Kingdom, but is often found in imported produce and is a serious pest of potato crops. The efficacy at 10°C of five fumigants was tested against diapausing beetles in the laboratory. Phosphine was the most effective giving 100 % kill in tests with a concentration time product of 6.7 g.h/m3; 100 % kill was also achieved in tests with: methyl bromide at 166 g.h/m3; carbon tetrachloride at 4000 g.h/m3; ethylene dichloride at 6240 g.h/m3; and 1,1,1‐trichloroethane at 11600 g.h/m3. A set of practical dosage schedules is given.