Susceptible ‘Newton’ and resistant ‘Abe’ winter wheat (Triticum aestivumL. em Thell.) were infested with larvae of biotype E Hessian fly,Mayetiola destructor(Say). Plants and crowns of infested ‘Newton’ weighed less, were shorter, had fewer tillers, and had significantly less soluble carbohydrates than the control plants. Only the plant height of infested resistant ‘Abe’ was significantly reduced. This finding was unexpected because avirulent larvae have never been shown to affect the growth of a resistant host. In ‘Newton,’ only the quantity of sucrose differed between treatments, being significantly greater in the infested than the control plants, although there was a trend for the control plants to have more fructan and less sucrose, glucose, and fructose than the treated plants. No differences were noted in soluble carbohydrates between infested and control ‘Abe.’ Ancymidol, a plant growth retardant, stunted both wheat cultivars but did not alter resistance in ‘Abe.’ Gibberellic acid (GA3) reversed ancymidol-induced growth inhibition but did not reverse Hessian fly stunting in ‘Newton.’ Therefore, stunting of wheat by the Hessian fly and ancymidol treatments appear to involve different biochemical pathways.