- The effect of the androgenic gland (AG) on female agonistic behavior was studied in the Australian freshwater crayfish Cherax quadricarinatus. Interactions between large males and smaller individuals of three types - sham-operated females, females implanted with the AG and intact males - were compared. Half-hour-long pair encounters were staged in large aquaria and monitored with a video camera. Interactions between crayfish of the same or opposite gender(s) were of a clearly agonistic character, without any courtship or reproductive elements. The large males were the winners of all fights. Small males fought more often and for longer periods of time, and grasped their male opponents for longer periods of time, than sham operated females. AG-implanted females occupied an intermediate position between the two genders in their fighting behavior. In addition, AG-implanted females performed I crawling over' (a tolerance-indicative act which is more pronounced towards the other sex) over the large males less frequently than the sham operated females did, and were also treated by these males more like males than females, with regard to this behavior. The behavioral changes in AG-implanted females followed the general trend of masculinization also evident in the morphological and physiological changes in their gonads and the appearance of male secondary sexual characters.