The populations of two frogs, Ptychadena maccarthyensis and P. oxyrhynchus, were studied over a four-year period in the Lamto savanna (Ivory Coast), where the climate is characterized by a dry season lasting from December to February, and a rainy season from March to November. P. oxyrhynchus breeds from February to May, while P. maccarthyensis does not breed before March but can continue to do so until October. Consideration of size-frequency histograms constructed from sequential samples in the two populations shows that the two species reach sexual maturity 8 to 9 months after metamorphosis, when the females attain a length of 43 mm for P. maccarthyensis and 59 mm for P. oxyrhynchus. There is very little overlap in adult size, either between sexes or species. Average clutch size is 1333 eggs in P. maccarthyensis and 3476 eggs in P. oxyrhynchus. The laying of a second clutch of eggs during the year has not been observed. However there is a strong probability that this does in fact occur, particularly in P. maccarthyensis which has a long breeding season. Fecundity is high in the two species studied. The mortality rate is high for eggs and young individuals, especially during dry years. Adult mortality is low.