The biochemical defence related responses conferred by Dn1 and Dn5 resistance genes in wheat against Russian wheat aphid (RWA) biotype 2 and biotype 3 in South Africa were investigated. The early responses of wheat to aphid investigation were determined and these included the activities of enzymes associated with the generation of reactive oxygen species (superoxide dismutase activity SOD and NADPH oxidase). The effect of aphid infestation on the activities of PR proteins was also determined. Biotype 2 and 3 infestation induced increase in enzyme activities of β-1,3-glucanase, peroxidase, NADPH oxidase and superoxide dismutase in the resistant wheat cultivar (PAN3144) hours post infestation, but a relatively lower enzyme activity of the uninfested plant of the resistant cultivar (PAN3144), susceptible uninfested cultivar (PAN3364) and the infested susceptible cultivar (PAN3364). These findings suggest that enzymes play a role as indicators in the RWA – wheat resistance response. The results obtained are consistent indicating that biotype 2 and biotypes 3 are virulent to Dn1 but, avirulent to Dn5 containing cultivars.