Table III. Maintenance of the undifferentiated non-phagocytic state requires both FGF4 and serum factor(s) and correlates with the proliferation potential of trophectoderm cells.

Culture medium	Total No. of embryosa	No. of embryos with
		0 bead	<10 beads	>100 beads
DMEM	12 (3)	0	0	12
DMEM + FGF4	36 (3)	0	0	36
DMEM + 15% fetal calf serum	20 (3)	0	0	20
DMEM + 15% fetal calf serum + FGF4 (25 ng/ml)	80 (4)	69	11	0

^aNumber of independent experiments in parentheses.