SUMMARYAdult bees of known ages from a disease-resistant line were tested for their behavioural response towards larvae infected with American foul brood. Eighteen colonies, each composed of adult bees of the same age to within 4 days, were tested one or more times when the bees were 4–68 days old. Results of two summers' work provide a basis for the hypothesis that colonies composed ofyoungresistant bees will remove all or nearly all larvae killed by foul brood regardless of nectar flow conditions, whereas colonies of the same resistant line made up of beesolderthan about 4 weeks remove the larvae only during a nectar flow.