This paper presents the results of X-rat fluorescence analysis of trace-elements for approximately 650 rimsherds from 16 prehistoric to historic Iroquoian sites extending from the St. Lawrence Valley as far west as Lake Huron. Attempts were made to measure similarities and differences in the chemical composition of Iroquoian ceramics between the St. Lawrence Valley and the area occupied by groups ancestral to the Huron and Tionontati; among individual St. Lawrence and Ontario Iroquoian sites; between Ontario and St Lawrence style sherds from the same Ontario Iroquoian sites; and among different longhouses within three Ontario Iroquoian villages. The findings indicate lines along which further research of this sort may prove valuable.