Summary Buprenorphine is a partial μ, κ agonist that has been shown to influence spontaneous behaviour in animals. Previously, we have demonstrated significant differences in the analgesic response to buprenorphine between the August Copenhagen Irish (ACI)/SegHsd and the Brown Norway (BN)/RijHsd inbred rat strains. The purpose of this study was to determine whether these strains also differed in their behavioural response to buprenorphine in order to provide an additional parameter for the genetic analysis and localization of genes involved in this response. Male and female rats of both strains were used ( n = 6/strain/sex) for this study. Each rat was subjected, respectively, to three treatment regimens at 15:00 h: (A) unchallenged; (B) intravenous saline; (C) intravenous buprenorphine (0.05 mg/kg) according to a crossover design. The relative duration (s/h) of locomotion, grooming, drinking and eating behaviour was subsequently determined from 15:30 to 07:00 h using the automatic registration system, Laboratory Animal Behaviour Registration and Analysis System™. Significant strain differences were observed in unchallenged behaviour between the ACI and the BN rats. ACI rats, but not BN rats, responded to buprenorphine treatment with decreased levels of locomotion, drinking and eating behaviour. The same treatment resulted in an increased grooming behaviour in both strains. Slight but significant sex differences were observed for locomotion and eating in the analysis of variance procedure, but did not reach the level of statistical significance in the multiple comparison procedure. The results of this study emphasize the possibility that strain-specific effects must be taken into account when using behavioural parameters for the assessment of the analgesic effects of buprenorphine in rats.