Quantification of the pro-angiogenic cytokine, vascular endothelial growth factor-D (VEGF-D), by ELISA has shown utility in the diagnosis, prognosis, and therapeutic monitoring of several cancers. The utility of VEGF-D quantification is particularly evident for lymphangioleiomyomatosis (LAM), a rare cystic lung disease. We are currently performing validation of a VEGF-D ELISA using sera from cases of confirmed LAM, and here we report our preliminary results.