This investigation was carried out to clarify the effect of synthetic LH-Releasing Hormone (LH-RH) on induction of ovulation in plaice, Limanda yokohamae, and goby, Acanthogobius flavimanus. Thirty seven mature female plaice weighing 123-291g (average 189g) were used in two experiments. In the first experiment, it was ascertained that 1 mg LH-RH dissolved in 0.2ml physiological salt solution could not induce ovulation, whereas 1mg LH-RH emulsified with complete adjuvant caused immediate increase in body weight and induced ovulation in all treated fish. A subsequent experiment was undertaken to discern the optimum dosage and sustaining effect of a single intramuscular injection of emulsified LH-RH. LH-RH at a dosage of 1mg induced ovulation in all fish (average 4.2days); 200μg resulted in ovulation in 4 of 5 fish (average 6.75 days); while 40μg had the same effect in only 2 of 5 fish (average 8.5 days). In the third experiment, 80 mature female goby weighing 32-76.5g (average 46.9g) were used. Emulsified 100 and 350μg LH-RH induced ovulation in 11 of 20 fish and in all fish, respectively. An aqueous solution of LH-RH 100μg induced ovulation in only 1 of 10 fish. Therefore, it is concluded that synthetic LH-RH can induce ovulation, and moreover, a LH-RH emulsion is more effective than an aqueous solution in inducing ovulation due to prolonged absorption.