Abstract Houseflies ( Musca domestica L.) were trained in a compound-conditioning paradigm where the conditioning stimuli were water and 1% sodium chloride solution. The unconditioned stimulus was 16% sucrose solution. A high degree of conditioning was produced. Control experiments for pseudoconditioning and sensitization revealed that the response of the flies to the procedure were due to an associative process. Experiments with double-water conditioned stimuli and with an interval between stimulus presentations indicate that the marked response to the first conditioned stimulus may be due to stimulus generalization in which the water, rather than the salt component of both stimuli served as the learning cue.