Although several senses are used in agonistic and sexual behaviours by Eublepharis macularius and Paroedura pictus, different cues do not have the same relative value for males of the two species. Behavioural patterns observed in the presence of anesthetized conspecifics of both sexes differed considerably. The agonistic and sexual behaviours of E. macularius underwent progressive changes in reaction time and the frequency and duration of other behaviours. Aggressive behaviour eventually almost completely disappeared in P. pictus and was replaced by sexual behaviour, whatever the sex of the stimulus-animal ; the lizards then appeared to be incapable of distinguishing males from females. Agonistic behaviour of both species was sensitive to the immobility of the conspecific, although to different degrees. These data concur with observations carried out under more natural conditions; sex recognition criteria differ between the species. E. macularius relies primarily on chemical signals for sex recognition and sex-related behaviours. In P. pictus, which depends primarily on visual signals, conspecific posture and behaviour are the main factors responsible for both sexual and agonistic reactions.