In vitroexperiments on late-larval stage fat body ofCorcyra cephalonicaindicate that treatment with 20-hydroxyecdysone (20-HE)alone does not alter the fat body acid phosphatase activity. However, a significant stimulation of fat body enzyme activity by 20-HE is noticeable when the hormone was added to the medium among with haemolymph obtained from the posterior half of the 24 h ligated late-last instar larvae. Haemolymph from the anterior half failed to show any stimulatory effect. The posterior haemolymph loses its stimulatory effect by heat, acid, alkali and enzyme treatments. These results suggest the presence of some factor(s) in larval haemolymph which potentiate the stimulatory effect of 20-HE on the fat body enzyme activity during late-larval development ofCorcyra.Furthermore, our co-culture studies reveal that these factor(s) are synthesis by the hind gut-associated lobular visceral fat body.