As a result of selection for high amylase activity in two strains of the flour beetle Tribolium confusum, mean activity considerably increased. Selection for low activity was ineffective in one strain, and mean activity increased, contrary to expectation, in the downward-selection line of the other. Heritabilities of amylase activity were 0.52 and 0.18 for the two strains (estimated by offspring-midparent regression in generation 1). Environmental factors have considerable effects on activity. The outcome of selection and possible models for the genetic control of amylase activity in Tribolium are discussed.