Abstract: The differential outcomes effect refers to the increase in speed of acquisition or terminal accuracy that occurs in discrimination training when each of two or more discriminative stimuli is correlated with a different outcome (e.g. type of reinforcer). The present study demonstrated this effect in domestic hens exposed to a titrating-delayed-matching-to-sample procedure, under which correct responses increased (and incorrect responses decreased) the delay between the offset of a sample stimulus and the onset of two comparison stimuli. Colors of key illumination (red, green) were used as sample and comparison stimuli and correct responses resulted in 1- or 4-s food deliveries. When 1-s food deliveries consistently followed correct responses to one key color and 4-s food deliveries followed correct responses to the other key color, the maximum delay reached by the hens and their overall accuracy was significantly higher than when 1- and 4-s food deliveries were randomly arranged following correct responses to both key colors. These data constitute the first demonstration of the differential outcomes effect in chickens, and in any species evaluated under a titrating-delayed-matching-to-sample procedure.