The larval stage of Haiuieniania hylae (Ewing) embeds in the California Tree Frog Hyla cadavciina Cope and Haunemania bufonis Loomis and Welbourn parasitizes the Red-Spotted Toad, Biifo punctatiis Baird and Girard at Fortynine Palms Oasis, San Bernardino County, Joshua Tree National Monument, California. Studies from May 1969 to April 1971 revealed estimated average populations of 288 frogs and 3C0 toads around three small ponds. Approximately 98.9 percent of the frogs had a mean of 21.4 H. hylae per frog and the estimated larval populations varied from 4250 in the spring to 8500 larvae in July to September. One life cycle is completed each year, but unengorged larvae were found on frogs throughout the summer. Nearly 41 percent of the toads possessed a mean of 8 H. bufonis and the estimated low was 840 larvae in May to July and the high was 1350 larvae in September. Only one life cycle per year was determined, and unengorged larvae were observed only in the late summer months.