The lymphatic system transports fluids and facilitating the return of extravasated cells and macromolecules back into the blood circulation. Obstructions in lymphatic vessel function, known as lymphedema, can occur as a primary or a secondary disorder. Milroy’s disease is an example of a genetic or primary lymphedema where mutations in one allele of the VEGFR3 gene leads to pervasive lymphatic malfunction resulting in the accumulation of fluids in the lower limbs. In zebrafish, this disorder can be modeled by mutations in this receptor or its ligand, VEGF-C. In secondary lymphedema, an injury to lymphatic vessels can occur after surgery, causing a blockage in the lymphatic system and fluid accumulation in affected tissues. In both cases, pressure and massage have been the only treatments over the last 200 years. To understand the signaling pathways that might be involved in inducing lymphedema, we investigated the ability of preclinical cancer drugs targeting the VEGFRs, MEPK/ERK or PI3K/mTOR to disrupt lymphangiogenesis. We found that MEK1/2 inhibition over a 6-hour period at 3 days post fertilization to provide a dramatic blockade lymphatic function that cannot be recovered by drug removal. To determine whether transgenic overactivation of these pathways may rescue this phenotype, we created 2 transgenic lines, using the fli1 promoter to drive endothelial expression. Treatment with the MEK1/2 inhibitor typically impeded the formation of the thoracic duct in greater than 80% of zebrafish larvae. In the transgenic fli1::MEK1DD line, this lymphatic vessel is effectively rescued. However, increased endothelial mTORC1 in a fli1::rhebS16H transgenic line had no effect. To provide further mechanistic insight into the signaling components required for proper lymphangiogenesis, we are currently examining the ability of a number of chemical compounds for their ability to rescue this phenotype.