In some vertebrates, calling activity is an attribute used by males to attract females during courtship. This behavior can be modulated by exogenous (physical) and endogenous (hypothalamic nonapeptides; Vasopressin/Vasotocin (AVT)) factors. During breeding, males of Boana pulchella, a South American hylid frog, congregate in choruses and emit three distinct note types. In this study, first we did continued recordings of calling activity, temperature, light intensity and rainfall using dataloggers during one year in a chorus of B. pulchella. Second, we looked for the presence of AVT in the brain of B. pulchella males throgh immunohistochemistry; and third, we performed pharmacological experiments in the field by injecting AVT in calling males. In the chorus, calling activity was more frequent in warmer seasons and not evenly distributed during the night. It peaked between 11 pm and 2 am and decreased significantly 2 hours before sunrise. Temperature and photoperiod, but not rainfall, were correlated with calling activity. We identified AVT neurons in the preoptic area using immunostaining and classified them into three types: parvocells, magnocells, and gigantocells. Our preliminary results show no change in call rate of males after AVT injection.