The effects of the doubly labelled water technique (intraperitoneal injection, temporary food deprivation and blood sampling) on the energy expenditure, food intake and behaviour of 18 white (MF1) mice was investigated. There were no significant differences in mean energy expenditure or food intake between experimental and control animals, on which the techniques were not performed, over the first 24 h after manipulation. These data indicate that there are no direct metabolic consequences associated with the procedures. During the 100 min immediately after blood sampling, the behaviour of experimental animals involved significantly more grooming, mostly at the site of the blood sample wound, more feeding and more general activity, at the expense of resting, when compared with controls. Twenty hours later the behavioural differences were less marked, but still statistically significantly different, and reversed: experimental animals spent more time resting and less in general activity or feeding. The effects of the technique on the behaviour of white mice had trivial consequences for their daily energy expenditure. This may reflect the restricted behavioural repertoire of these captive animals within respirometry chambers. The effect on wild animals may be more profound and requires investigation.