Vascular endothelial growth factor (VEGF) i s required for vascular development. In the quail, four VEGF isoforms formed by alternative splicing, are translated into proteins with 122, 146, 166, and 190 amino acids. VEGF isoforms differ biochemically, with variable affinities for heparan sulfate proteoglycans, the extracellular matrix and VEGF receptors. There are few data on the functional significance of VEGF isoforms. RT-PCR was used to examine isoform expression during quail vascular development. Our results suggest that all quail isoforms are expressed during establishment of the vascular pattern in whole embryos and extraembryonic tissues at apparently equal levels. No isoform-specific expression patterns were detected in isolated endoderm or between embryo halves.