A reproductive strategy may be viewed as the combination of physiological, morphological, and behavioral traits that act together to produce the optimal number of offspring under given environmental conditions (Duellman and Trueb, 1986). Thus, different strategies can increase the efficiency or minimize the costs and/or risks associated with reproduction (Harvey and Pagel, 1993). Reproductive effort is an important component of a reproductive strategy because it allows one to measure the costs of reproduction (Stearns, 1992). A great diversity of anurans occur in the American tropics (Duellman, 1988). Nevertheless, there are few detailed studies on the reproduction of these anurans and studies focusing on reproductive effort are even rarer (e.g., Lampo and Medialdea, 1996). For the Pantanal, a great flat plain with an area of approximately 140,000 km2 in southwestern Brazil, there are only preliminary studies on the composition of the anuran fauna and few comments on their reproductive biology (Lutz, 1946, 1972). Based on comparative morphology and behavior, Heyer (1969) divided the genus Leptodactylus into five species groups, where L. chaquensis Cei belongs to the 'ocellatus' group and L. podicipinus (Cope) to the 'melanonotus' group. According to the classification of Duellman and Trueb (1986), L. podicipinus and L. chaquensis have the same reproductive mode: eggs inside a foam nest on the surface of ponds with aquatic feeding larvae. Leptodactylus chaquensis occurs in Argentina, Paraguay, Uruguay, and Brazil (Frost, 1985) and L. podicipinus is found in open formations of Paraguay, Argentina, Bolivia, and central Brazil (Heyer, 1994). In spite of the wide geographical distribution of these species, information about their reproductive biology is scarce (Vizotto, 1967; Gallardo, 1987; Martins, 1996; Rossa-Feres and Jim, 1994, 1996). Our aim was to study the reproductive strategies of L. chaquensis and L. podicipinus, which are very common in the study area. We investigated the reproductive period of each species, breeding sites, clutch and egg sizes, reproductive efforts, effects of female body size parameters on reproductive potential, and the occurrence of parental care and sexual size dimorphism. Data were collected monthly from December 1996 to January 1998. Adults of L. chaquensis and L. podicipinus were hand-captured at night near ponds and flooded areas at Base de Estudos do Pantanal-Universidade Federal de Mato Grosso do Sul (57?00'W; 19?34'S), in the municipal district of Corumba, State of Mato Grosso do Sul, Brazil. The climate is hot and humid, with a dry period from May to September and a rainy season from October to April. Seasonal floodings are common in the area from January to April. Reproductive period was determined based on calling activity of males, presence of amplectant pairs, and/or tadpoles. Breeding sites were characterized according to water depth, presence or absence of vegetation, and type of water body, which were classified as puddles, flooded areas, or permanent ponds. Occurrence of parental care was based on direct observations of the behavior of adults relative to nests and