Scholars in both the social and natural sciences have long debated the origin  and antiquity of maize in western South America.  This analysis presents  archaeological data from settlement survey and excavations, ethnobotanic data  and isotope analyses of Valdivia Phase skeletons to directly address current  issues regarding the origin and early role of maize in western South America.   Archaeological survey of pre-Hispanic occupation in El Oro Province, Ecuador  indicates a significant shift in site location corresponding to adaptive  changes near the end of the Early Formative Period reflecting an emphasis to a  more agricultural way of life.  Archaeological excavations of a earthen  platform mound at the Valdivia ceremonial center of La Emerenciana, 14C and  AMS dated to between 2203 and 1679 B.C., have uncovered numerous pre-Hispanic  features consisting primarily of ritual offerings and burials.  Carbon  residues from the interior surfaces of Valdivia pottery contained in such  features were analyzed for the presence of opal phytoliths.  Three of the ten  samples analyzed contain phytolith assemblages representative of maize cob  chaff.  An isotope analysis of Valdivia skeletons from La Emerenciana supports  the archaeological and ethnobotanical evidence for an increase in C4 plant  consumption.  Bone isotope data of Valdivia skeletons from earlier in the  cultural sequence are compared and combined with the isotope evidence from La  Emerenciana and from later culture phases in the Ecuadorian sequence to  provide a basis for evaluating when maize was introduced into western South America and consider its possible early role in Andean prehistory.  The  results indicate that maize was introduced into coastal Ecuador during the  final portion of the Valdivia culture sequence and may have been integrated  into the subsistence economy as a ritual rather than staple food.