Two semi-cultivated Solanum species (S. sessiliflorum Dunal and S. stramonifolium Jacq.) are utilized by the Amazonian Indians of the Upper Orinoco Basin in Venezuela. The manner in which they have become partially domesticated by the Piaroas and other native tribes of this rain forest region is elucidated in the following text. Both species have two varieties, with and without prickles, the latter being the result of human selection. Patterns of indigenous utilization of these species brought to the selection of morphologic forms and to the differentiation of karyotypes of varieties, and exploitation of the species also reflects in the perception of them among users. S. sessiliflorum is cultivated in swiddens and has an economic role, whereas S. stramonifolium is grown in dooryards. This difference is detectable to the Piaroas, as they recognize in their folk taxonomy three different varieties of S. sessiliflorum and one of S. stramonifolium, according to the stage of domestication of the species and the way in which they are utilized.