In the freshwater prawnMacrobrachium kistnensis reared with males, the ovarian development occurred normally, whereas it was delayed in the absence of males. Testis and vas deferens extracts when added to the water in which females are being reared brought about normal development of ovary in comparison to those which were reared in boiled water or ‘female water’ alone. Therefore, mature males appear to be producing a pheromone which is necessary for the ovarian development of the female and the source of this might be vas deferens or testis. On the other hand, the central nervous tissue extracts stimulated vitellogenesis in oocytes. In particular, the brain extracts were more effective than those of thoracic ganglion in inducing this response. Thus, in the present study ovarian maturation and vitellogenesis appear to be under the pheromonal and hormonal controls.