From the present study it appears that castrated male rats can be made attractive to intact males by estradiol benzoate plus progesterone (EB + P). For the determination of attractivity a residential plus-maze was used in which the resident male could choose between the company of the experimental male and that of an ovariectomized female with or without EB + P. In one experiment the males were castrated in adulthood; these animals were less attractive than the ovariectomized females with a similar hormone treatment. In a second experiment it was found that males that had been castrated at birth were as attractive as the ovariectomized females, after treatment with EB + P. These findings indicate that the attractivity that can be induced by EP + P in gonadectomized adult rats is somewhat but not wholly reduced if androgen is present during the neonatal period.