The life cycle of Echinostoma rodriguesi, a new 37-spined echinostome from Brazil, is de- scribed. One sporocyst generation and at least two redial generations developed in the first interme- diate host, Physa rivalis. The same physid snail, or the planorbid snail, Biomphalaria glabrata, served as the second intermediate host in the laboratory. Adults were obtained from experimentally infected chicks, pigeons, hamsters, and mice.