Adult male mice (Mus musculus) which have a prior history of experience with other adult male and adult female mice readily produce 70 kHz ultrasonic vocalizations in the presence of urine from adult females but not in the presence of urine from adult males. Urine from immatures of either sex does not elicit ultrasounds from socially experienced adult males. The ultrasound eliciting potency of adult male urine was not improved substantially following castration of adult males, injection of testosterone propionate to castrated adult males, administration of estradiol benzoate to castrated adult males, or neonatal castration. Ovarian hormones do not appear to be necessary for either the appearance at puberty, or the maintenance during adulthood, of the ultrasound eliciting cues of female urine. Stage of estrus did not have a major modulating effect on urinary cues eliciling male ultrasounds. Treatments that did not substantially reduce the signal value of adult female urine include ovariectomy before or after puberty, ovariectomy with adrenalectomy, and neonatal administration of testosterone. The administration of testosterone to ovariectomized adult females, and hypophyseclomy, virtually eliminated the ability of urine from adult females to elicit ultrasounds from socially experienced adult males. The implication of pituitary hormones in the modulation of female urinary cues thai elicit ultrasounds is particularly interesting since pituitary factors are also implicated in the proximal causation of postparturient maternal aggression, which adult male ultrasounds may function to moderate.