Quantitative analysis of endothelial sprouting in response to FGF2 and VEGF. CJ7 ES cells were first induced to differentiate at day 0 in the presence of both VEGF (50 ng/ml) and FGF2 (100 ng/ml). For the second growth factor addition at day 6, VEGF (50 ng/ml) and FGF2 (100 ng/ml) were added alone or in combination. The mean total sprout length of EBs exhibiting endothelial sprouts (angiogenic EBs) was measured at day 11, after CD31 immunostaining, and image analysis with MetaMorph Offline software. Data represent the mean values ± SD resulting from at least 25 angiogenic EBs obtained in one differentiation experiment.