The well-characterized Tecumseh population was utilized as a first step in determining genetic linkage to hypertension, using the quantitative trait locus (QTL) approach. A total of 250 white sibships in the Tecumseh population were examined using 400 anonymous markers and candidate genes. Approximately 100 markers that demonstrated linkage were used to examine 250 African-American sibships in Maywood, Illinois. Fifty refined candidate markers were used to study several extant Black populations in Jamaica and Nigeria, as well as individuals in the other two populations. A unique feature of the network is the inclusion of a rat genotyping center. Crosses of inbred hypertensive and normotensive rats are used to identify genomic regions linked to hypertension. The regions are then used to identify homologous human candidate genes in addition to those already selected from previous research.