The life-cycle of Tremiorchis ranarum Mehra and Negi, 1926 (Trematoda: Plagiorchiidae) infecting Rana tigrina and R. cyanophlyctis is elucidated. Life-cycle stages, from egg to egg-producing adults, were successfully established in the laboratory. Life-cycle took more than two months for completion. Cercariae were found in the snail, Pila virens collected from paddy fields at Chelembra in the Malappuram district of Kerala during the monsoon months. Cercariae are of the xiphidiocercous type. Metacercariae occurred beneath the skin and in head, tail and body musculature of tadpoles of R. tigrina and R. cyanophlyctis. Adult frogs are refractory to cercarial infection. Frogs became infected when they fed on tadpoles containing metacercariae. Successive stages in the development to adult from the metacercariae were followed. Chronological synchronization in the reproductive activity of the host and the parasite is briefly discussed.
