Fertile chicken eggs (Gallus gallus domesticus), 16 containing 2-d emb
ryos and 16 containing 9-d embryos, were exposed to a microgravity env
ironment during a 5-d space shuttle flight (Discovery, STS-29, March 1
989). The 9-d flight group embryos continued their incubation to hatch
at 21-d, revealed no gross abnormalities, and developed normally to a
dults. Embryos of the 2-d group did not survive the 5-d mission. Synch
ronous controls for both age groups survived, hatched, and developed t
o adults. This result supports an hypothesis that a gravity field fact
or acts in the cellular and/or intercellular microenvironment during t
he development interval 2-7-d in the chick embryo.