Behavior analysts refer to a decrease in response rate following repeated, contingent presentations of a reinforcing stimulus as a product of satiation. Other evidence suggests that these decreases may often be due to habituation to the sensory properties of the reinforcing stimulus. The investigation reported here sought to determine whether decreases in operant responding by 3 adults with developmental disabilities were due to satiation or habituation. During baseline, participants placed poker chips into a container, and no reinforcement was available. Within subsequent phases, participants received diet lemon-lime soda on a fixed-ratio (FR) schedule of reinforcement. In one condition, the color of the soda was constant throughout the session, and in another condition food coloring was added several minutes into the session. Results for at least 2 participants indicated that: (a) soda functioned as a reinforcer for placing poker chips in the can; (b) response rates decreased within the session to baseline levels; and (c) response rates increased following a change in the color of the soda within the session. Results for the third participant were less clear. The results support the argument made by other researchers that the terms habituation (a weakening of a behavior following contact with the reinforcing stimulus) and stimulus specificity (a strengthening of a behavior following a change in the reinforcing stimulus) may be more appropriate descriptors of within-session changes in responding. The factors associated with habituation and satiation, as well as both basic and applied research examples, are discussed.