Angiostrongylus costaricensis eggs were successfully cultured to first stage larvae ina chemically defined medium. The most suitable medium for development was Ham's F-12 among seven chemically defined media and 10 serum supplemented media examined. The addition of serum to Ham's F-12 did not provide any further benefits for egg development. When tile eggs were cultured in this medium under 8% CO 2 in air, they developed and formed larvae inside tile eggs 5 days later. Thereafter, the eggs began to hatch to first stage larvae. Ten days after cultivation, 33% of the eggs had developed to first stage larvae. When these first stage larvae were infected to tile snail intermediate host, Biomphalaria glabrata, they developed to third stage larvae.