Human embryos cryopreserved after in-vitro fertilisation can be stored initially for 5 years, and the storage period may be extended to a maximum of 10 years. Of 1344 embryos cryopreserved between 1988 and 1994 at two centres in Manchester, 67% (904 embryos) have had to be destroyed at the end of the first 5-year interval, even if the couples involved remain childless.