1. A large proportion of virgin female guppies, Poecilia reticulata, are highly responsive when first placed with actively courting males. This responsiveness wanes over several days if a female is repeatedly exposed to male courtship in a standard test situation (15 mins./day on alternate days). The decline in response occurs even though copulation is prevented by presenting males which have been gonopodectomized (gonopodium removed). Many females become responsive again for a short period(s) some time after the initial period of receptivity at the start of testing. Examination of individual records of females tested for up to 6 weeks suggests that there are cycles in responsiveness which correspond closely to the 20-21 day cycle in receptivity demonstrated in nonvirgin fish (Liley, 1966). The data indicate that a virgin female is likely to be initially highly responsive whatever the stage of her endogenous cycle, hut after involvement in courtship a cycle in responsiveness becomes apparent. 2. Naive virgin females were highly responsive when first tested 2, 10 or 24 days after ovariectomy (Experiment 2). However in contrast to intact fish there was no reappearance of receptive behaviour after sexual activity observed at the start of testing had waned. 3. The rate of decline in responsiveness of naive virgin females is to some extent dependent upon the courtship testing regime (Experiment 3). Most females tested with gonopodectomized males for 20 minutes per day had become unresponsive by the 6th or 7th day; receptivity of females tested at 3 and 6 day intervals declined more slowly but eventually reached the same level as fish tested every day. Testing females with intact males on the first three days resulted in a more rapid drop in female responsiveness. Ovariectomized females were less responsive and their receptively waned more rapidly than intact females. 4. In experiment 4, an attempt was made to determine whether the high initial responsiveness of virgin females was due to the fact that they had been deprived of social stimulation provided by males. Virgin females were tested with gonopodectomized males on 8 consecutive days during which their receptivity declined to a low level. Females were then isolated from males individually or in groups for 1, 2, 3, 4 or 6 weeks before being retested with gonopodectomized males. There was no recovery of responsiveness to a level typical of naive virgin fish in the previously isolated females. Any recovery of responsiveness which did occur was that which might be expected on the basis of each female having the potential to undergo a cycle in receptivity related to an endogenous cycle of approximately 20 days. 5. It is concluded that there is a cycle in receptivity in virgin females which reflects an endocrine cycle in ovarian activity. In addition naive fish show an initially high level of response which is not dependent on the immediate ovarian hormone state and masks the cycle regulated by the ovary. The responsiveness of naive fish habituates as a result of exposure to male courtship. It is suggested that the interaction between the decremental effects (habituation) induced by courtship and the incremental effects of ovarian hormone and short-term incremental effects of courtship may interact in a manner which adjust female receptivity to the social environment, terminating sexual responsiveness once insemination has occurred a number of times.