Field studies on seed dispersal by fish in inundated Amazonian vegetation were carried out in a varzea forest of the Rio Madeira in Humaita, Amazonas, Brazil. Of the 33 plant spp. studied, 16 had seeds or fruits regularly dispersed by fish. In 17 spp. the seeds were usually destroyed when eaten. Seeds dispersed by fish belong to flowering plant groups which are relatively primitive, whereas those that are destroyed are more advanced; a result which confirms that ichthyochory is an archaic form of dispersal within primitive angiosperms that has been maintained in inundated tropical regions. The high frequency of ichthyochory is associated with nutrient-poor Amazonian waters, where fish depend substantially on allochthonous material, e.g., seeds and fruits which fall into the water. The homogeneity of the inundated vegetation in Amazonia may be the result of migratory fish dispersing diaspores.