The filarial worm, Litomosoides carinii (Travassos, 1919), Chandler, 1931, occurs naturally in the pleural cavities of wild cotton rats (Sigmodon hispidus). Vaz (1934) and Bell and Brown (1945) have reviewed the synonymy of L. carinii and list the rodents in which the worm has been naturally found. Laboratory rodents have been investigated as possible experimental hosts by several workers. Hawking and Burroughs (1946) have reported infection and the production of microfilariae in piebald rats, hamsters, and mice. Since the first report of this infection in white rats by Chandler (1931), several workers have reported on the white rat as a host for L. carinii (Scott and Cross, 1946; Scott et al, 1946; Scott, 1947; Williams and Brown, 1946; Williams, 1948; Bertram et al, 1946a, 1946b; Bertram, 1947). These workers appear to regard the white rat as as unsuitable host for this infection.