The theoretical possibility of applying gene transfer methodologies to the human 
germline is explored. Transgenic methods for genetically manipulating embryos 
may in principle be applied to humans. In particular, microinjection of 
retroviral vector appears to hold the greatest promise, with transgenic primates 
already obtained from this approach. Sperm-mediated gene transfer offers 
potentially the easiest route to the human germline, however the requisite 
methodology is presently underdeveloped. Nuclear transfer (cloning) offers an 
alternative approach to germline genetic modification, however there are major 
health concerns associated with current nuclear transfer methods. It is 
concluded that human germline gene therapy remains for all practical purposes a 
future possibility that must await significant and important advances in gene 
transfer technology.