Aryl hydrocarbon hydroxylase and glutathione S-transferase activity was determined in post-mitochondrial fractions of the mite Varroa jacobsoni (Oudemans) and the honeybee (Apis mellifera). Aryl hydrocarbon hydroxylase activity in the mite was about a third of that found in the honeybee, whereas the glutathione S-transferase activity was similar in the two. The results obtained may be relevant to the screening of acaricides to control the mite.