SummaryTwo genetic lines of bees were used to study removal from the nest of brood killed by cyanide. The Brown line, resistant to American foul brood, removes dead brood promptly, and is called hygienic. The Van Scoy line is susceptible to American foul brood, removes dead brood very slowly, and is called non-hygienic. Control colonies having both young and old bees from a single line responded to dead brood as expected: Browns were fast removers and Van Scoys were slow, regardless of the presence or absence of a nectar flow. Likewise“mixed”colonies, having foragers (old bees) of the Van Scoy line and hive bees (young bees) of the Brown line, quickly removed cyanide-killed individuals from the brood nest under both dearth and nectar-flow conditions. Mixed colonies with foragers of the Brown line and hive bees of the Van Scoy line removed cyanide-killed individuals from the brood nest very slowly in the absence of a nectar flow, but much more rapidly during a flow. Both young and old Brown bees concentrated on an area of comb containing dead brood in greater numbers than expected from their frequency in the whole colony. It is concluded that Brown foragers in mixed colonies engage in removal of dead brood during a nectar flow but not during a dearth.