Culture of 91/2-day rat embryos in human serum supplemented and unsupplemented with rat serum.

We attempted to grow explanted 91/2-day rat embryos in vitro in human serum but were unable to demonstrate normal growth as has been previously described. The embryos were consistently smaller, anaemic, and frequently deformed. These abnormalities were overcome by supplementing the human serum with 10% rat serum. The latter possibly provides yet unidentified essential growth factors required by rat embryos that are not present in human serum.