A method for cryopreserving bivalve oocytes, particularly those of Pacific oysters, by preparing a solution of a cryoprotectant in water, combining this with the oocytes, carrying out a first cooling step to a temperature of about -4.degree. C. to -20.degree. C., and carrying out a second cooling step to a temperature of about -25.degree..degree.C. to -55.degree. C.