Field experiments with the green peach aphid on tobacco were conducted at Blackstone, Virginia in 1983 and 1984. The objectives were to: 1) confirm and identify source materials resistant to the green peach aphid; 2) study the inheritance of aphid resistance; 3) verify heritability of resistant genotypes through F2 and advanced generation testing and 4) investigate the nature of the resistance. Results showed green peach aphid resistance in Tobacco Introductions 1462, 1118, 1112, 1024, breeding line 1-35 and cultivar NC 745. Inheritance studies showed that the resistance is a recessive trait controlled by three separate, non-linked loci; such that a homozygous recessive at any one locus will condition for the resistance reaction. Among the source materials, one locus conditioned the resistance shown by TI 1118, TI 1112 and breeding line I-35. A second independent locus conditioned the found in TI 1024 and a third independent locus conditioned the resistance observed in NC 745. Tobacco Introduction 1462 possessed alleles for resistance at both the second and third loci. Small aphid cages were of questionable value for studying the resistance reaction. Higher leaf temperatures were noted for the caged leaf surfaces and may be responsible for the unreliable results. Evaluation of F2, F3, F5, F5 populations developed from resistant x susceptible crosses indicated that aphid resistance is a heritable trait and is not closely linked to adverse agronomic quality characteristics. / Master of Science