In the great majority of amphibians yet investigated the occurrence of oocytes with more than one nucleus or more than a single liieiotiC figure is exceptional (Humphries, 1956,1966 ; Parnienter, Derezin andParnienter, 1960 ; Humphrey, 1963) . In the tailed frog Asca/'hus (mel, however, Macgregor and Kezer ( 1970) found that oogenesis regularly involves oocytes with eight nuclei, all but one of @yhich disappear before the final stages of oogenesis. When a related species, Leiopelnta hochstetteri, was investigated by Robinson, Stephenson and Stephenson ( 1973) , onlya single binucleate oocyte wasfoundamong 26oocytes examined. In the present paper the occurrence of niultinucleate stages as a regular feature of oogenesis in several genera of marsupial frogs of South America is reported. The multinucleate condition is associated with the early stages of oogenesis; in large, yolky oocytes only one nucleus is present. Most of the marsupial frogs are inhabitants of the humid forests of South America. In these frogs the aquatic larval stages are reduced or eliminated al together, a phenomenon associated with the fact that the female carries the em bryos on her back, either within a pouch of integument or in shallow depressions of the skin. The genera Flectonotus, Cast rotheca, and Amphignathodon are char acterized by pouches, while in Frit@iana, Crvptobatrachus, Ste fania and Henti phractus the embryos are carried in depressions of the skin. For a list of these frogs with locality and references of taxonomic interest see the work of Duellman (1976). Relatively little information is availal)le regarding reproduction and development in marsupial frogs. The relationship between mother and embryos has been studied in some detail in Gastrotheca riohanzbae, a species that carries the embryos in the potich up to the tadpole stage (see del Pino, Galarza, de Albtija, and Hum phries, 1975, for references). Among the species of Gastrotheca that carry the embryos to the young froglet stage, Gastrotheca ovif era is the best known (see Mertens, 1957, for a description of its life history and references). This report describes some features of oogenesis in 33 species of marsupial frogs that correspond to the described species of Ainphignathodon and Henzi phractus as listed by Duellman (1976), to two (of three) species of Flectonotus, one (of six) species of Stefania and 20 (of 32) species of Gastrotheca. In addi tion, the ovaries of three unnamed species of Gastrotlieca were also analyzed. The peculiarities of oogenesis have been studied in more detail in Flectonotns pvgmaeus, Gastrotheca ovif era and Gastrotheca sp., an unnanied species from Venezuela, since in these instances both living and preserved specimens were available. Living specimens of C. niarsupiata, G. excubitor, C. niertensi and C. plum bea were also