A review of current in vivo testing systems and procedures used for assessing reproductive and heritable genetic hazards of chemicals is presented. A comparison is made between the similarities and differences in protocols for reproductive effects among the different regulatory agencies in the United States and countries belonging to the Organization for Economic Cooperation and Development. Uses of in vivo mammalian mutagenicity data for assessing potential human heritable genetic diseases risk are also discussed and examples of how various in vivo mutagenicity test systems can be used to estimate risk are presented along with explanations of the various assumptions employed.