A chemical library screening strategy to identify small-molecule modulators of vascular development in Xenopus embryos. Xenopus embryos were arrayed in multiwell plates, and single compounds from the LOPAC¹²⁸⁰ chemical library were added to the water in each well. Embryos were screened visually for developmental defects (edema and/or late lethality). Positive hits are verified by repeating the phenotypic assay. Compounds interfering with vascular development are identified by whole-mount in situ hybridization of compound-treated Xenopus embryos.