An apparatus is described that automates the elicitation of the proboscis extension reflex (PER) in dipterans. The PER has been used as a measure of both classical conditioning and central excitation. Most studies of PER have employed manual stimulation, which adds inter- and intraexperimenter differences in technique as another source of variance. The advantages of this apparatus are (1) elimination of individual differences in manual techniques of experimenters as a possible source of error variance and (2) capability of stimulating several flies individually during a single session. An experiment is reported comparing the manual and automated methods.