Abstract: AIM: To study the polymorphism of the development of Paragonimus heterotremus in rats and to ascertain the host nature of the rat. METHODS: SD and Wistar rats were each infected orally with 100 metacercariae of P.heterotremus . The distribution and development of the worms recovered from rats 14-156 days after infection were observed. RESULTS:Thirty days after infection, reproductive organs appeared in the worms recovered from the body cavities.Seventy days after infection,worm cysts were found in the lungs, livers and pleural wall, the worms in the cystsmatured but the worm s detected in the muscles were still stunted on the 156th day after infection. CONCLUSION: Rat is the definitive host and paratenic host of P. heterotremus. The development of P. heterotremus is polymorphic.

Key words: Paragonimus heterotremus, rat, definitivehost, paratenic host