Three pigeons responded to a color display on the center key of a three-key chamber. Following completion of a fixed ratio schedule, the display changed to a vertical line and subjects had to complete a fixed interval schedule (FI) after which the center key was darkened and both side keys illuminated. The correct side key was determined by both the color of the initial stimulus and the duration of the FI. Pigeons were able to discriminate successfully when the color changed between sessions and durations changed within sessions, when color changed within sessions and duration changed between sessions, and when both color and duration changed within sessions. The FI component served simultaneously as a retention interval and a discriminative stimulus.