Past research in our lab has shown that pleasant odours decrease the intensity of pain perception (Marchand & Arsenault, 2002). Olfactive experiences, therefore, appear to change pain perception. In this previous study, the subjects were inhaling different odours from bottles, possibly causing a bias due to analgesic expectations of the subjects. Unfortunately, no study has ever tested the effects of odours on pain in a single-blind testing paradigm (i.e., when subjects are unaware that odours are being manipulated). Our objective was to evaluate the influence of a citrus odour, diffused without the knowledge of volunteers, on pain perception as well as to verify if this diffusion changes the strength of diffuse noxious inhibitory controls (DNIC). Thirty healthy subjects (15 women) participated in two standardized tests on 2 different days; one with diffusion of lemon essential oil and the other without. Testing consisted of a 2 minute thermal stimulation period (with a small thermode) repeated twice, once before and once after having triggered DNIC. Participants immerse their arm in a bath of cold water for 2 min (10°C) to trigger DNIC. Results showed that the scent of lemon decreased perceived pain by as much as 13% (p=0,02). Moreover, based on questionnaire on lab environment, no significant report of the presence of odours was recorded, suggesting that the effect was not related to expectations nor distractions. Lemon scent had no effect on the strength of DNIC, suggesting the recruitment of a different endogenous pain inhibition mechanism. The diffusion of a pleasant odour could be applied in private clinics and in various medical facilities in order to support an optimal level of pain relief.