Ultrasounds of a lost mouse pup release pup approach in adult mice and lead to pup retrieving if parental motivation is sufficient. Here, we investigate the effects of oestrogen and progesterone and parental experience on ultrasonic key-stimulus preference and on pup retrieving. Tests with various groups of inexperienced, pup-experienced, gonadectomized and hormone treated females and males lead to the following major results: Female sex hormones are not necessary for establishing maximum retrieving rates in mice experienced with pups, they are necessary for spontaneous retrieving to occur in inexperienced mice, they support the achievement of experience with pups and, if present during the time of formation of experience, lead to a superior and prolonged performance of retrieving and ultrasonic key-stimulus preference. Ultrasound discrimination does not occur spontaneously but only in mice experienced with pups. It is suggested that parental motivation sensitizes selective attention for pup cues and thus makes ultrasound preference possible. Parental motivation is regarded as a state in which the salience of releasing stimuli from the pups is selectively enhanced through hormones and long-lasting internal changes induced by experience with pups.