The teratogen thalidomide was removed from the market in the 1960’s when studies showed that female exposure during pregnancy resulted in severe limb deformities and other malformations in children. How paternal exposure affected these outcomes remains unknown. Sea urchin embryos serve as model organisms for early deuterostome development since they share many highly conserved developmental pathways with humans. After spawning and fertilization of Lytechinus pictus (L. pictus) embryos, experiments followed two different protocols. Triplicate cultures of embryos were incubated (17°C) with thalidomide (400µM) dissolved in DMSO. The other approach involved fertilizing eggs with thalidomide pre-treated sperm (0.39µM). Pre-treatment involved incubation of sperm (17°C) for one hour, then triplicate culturing of the embryos in sea water. Both protocols were analyzed at 24, 48, and 72 hours post fertilization for abnormal development. Embryos fixed at 48 hours were stained using immunohistochemical staining techniques to observe serotonergic and cholinergic neurons. Swimming behavior orientation will be observed using a light test at 72 hours. Preliminary results at 24 hours suggest similar percentages of abnormalities in the controls for both protocols (10%).  Embryos treated in culture exhibited 59% abnormalities. Embryos resulting from fertilization with thalidomide pre-treated sperm also exhibited abnormalities, but at a lower level (28%). Previous studies in lab show reductions in serotonergic neurons in embryos treated with thalidomide and embryos fertilized with thalidomide pre-treated sperm. It is anticipated that embryos exposed to thalidomide in either protocol will demonstrate a reduction in cholinergic neurons. Data from lab indicates that embryos treated with thalidomide or resulting from fertilization with thalidomide pre-treated sperm do not exhibit the directional response to the light as control groups do. We expect fewer embryos to orientate towards light due to thalidomide exposure. Our studies suggest that both maternal and paternal exposure to thalidomide can result in abnormal embryogenesis.