Gene diversity and genetic structure of tribal populations of Andhra Pradesh, India, have been analyzed under a hierarchical model consisting of five regions of the state, tribes within the regions, and local subpopulations within the tribes. Average gene diversity has been estimated from gene frequency data for 15 polymorphic loci by using nested gene diversity analysis of GST. The intralocation coefficient of gene diversity was estimated at 96% of the total, whereas the intertribal, within--and between--regional gene diversities were found to be only 1.90, 0.95, and 1.43%, respectively. The estimate of gene diversity was higher for loci with higher degrees of polymorphism such as ABO, MN, ESD, and PTC and lower for loci with low-level polymorphism and extreme gene frequencies such as Hb, Tf, PHI, 6PGD, and Hp. The nature of selective preference or neutrality at the loci seems to be important in this respect. Tribes of the plains exhibit the least gene diversity, apparently because of higher gene flow among them. The contribution of loci with intermediate gene frequencies in intertribal and regional gene diversity was found to be higher than for loci with extreme allelic frequencies. These results suggest that the most significant component of variation is between individuals within locations and that variation between local subpopulations is negligible in the genetic structure of a population. Forces like selection, gene flow and drift also influence the diversity depending upon the nature of the locus.