The flowering and fruiting phenology, floral biology, pollination ecology, and breeding system of the emergent tree Ceiba pentandra were studied in the Brazilian Central Amazon. Of the 21 trees studied, 17 flowered once or twice during the 6-y study period. The mass flowering and relatively high production of nectar per flower (mean of 310 µl) resulted in a high nectar production (over 200 l per tree per season). Flowers were visited by a wide range of nocturnal (bats, marsupials, night monkeys, hawk moths) and diurnal (bees, wasps, hummingbirds) animals, but only phyllostomid bats, especially Phyllostomus hastatus and Phyllostomus discolor, played a relevant role promoting cross-pollination. Pollinations which occurred in the early morning by diurnal floral visitors were ineffective since pollen tubes did not traverse the style and reach the ovary before stylar abscission. Despite the apparently normal growth of the self-pollen tubes, controlled pollinations carried out in one tree revealed no fruit set by selfing and 16.8% fruit set by crossing. Progeny analysis from this 'self-incompatible' tree using isozyme markers showed that fruits resulting from mixed-pollination (i.e., 50% self-plus 50% crosspollen on the stigma) set only 1.6% of selfed seeds. The percentage of outcrossed seeds in fruits resulting from open-pollination in two neighbouring planted trees, which flowered in isolation and concomitantly, was estimated at 91% and 71%. Two isolated trees did not set any fruits despite massive flowering, whereas two others set large quantities of seed, supporting data in the literature stating that variable degrees of self-fertility may occur in this species. RESUMO. A fenologia de floração e de frutificação, a biologia floral, a ecologia de polinização e o sistema reprodutivo da árvore emergente Ceiba pentandra foram estudados na Amazônia Central Brasileira. Dezessete das 21 árvores estudadas (doze nativas e nove plantadas de sementes de procedência desconhecida) floriram uma ou duas vezes cada uma durante os seis anos do estudo. A maior parte das árvores nativas floriu massivamente somente em 1993 e 1996, enquanto que algumas das árvores plantadas floriram massivamente somente em 1992 e 1997. 247