The experiments reported in the present study tested whether decreasing intertrial intervals (lTls) intensifies the disruptive effects of increasing retention intervals (RIs) in a delayed conditional discrimination by decreasing the animal's trial tracking accuracy (Cohen & Armstrong, 1996;Cohen & Roberts, 1996). Rats responded on a fixed ratio (FR) 1 or fixed interval (FI) lO-secreinforcement schedule at a second light or tone stimulus, 82, when the first light or tone stimulus, 81, had signaled an FI lO-secor FR 1 schedule, respectively. RIs between 81 and 82 were increased from 3 to 24 sec and never exceeded ITls that were reduced from 24 to 6 sec. For some rats, the trials were separated from each other by extending the lever at 81 and retracting it at the end of 82 (lTI lever-retracted group). For other, control rats, the lever remained extended throughout the session (lever-extended group, Experiment 1) or was extended and retracted with the onset and offset of each stimulus (RI/ITI leverretracted group, Experiment 2). The rats under all trial conditions learned to delay leverpressing on the FI lO-sec schedule. Latency to begin leverpressing on the FI lO-sec schedule declined as RIs were increased, but this effect was attenuated in the ITI lever-retracted groups in both experiments, as would be predicted by the trial tracking hypothesis. Decreasing ITls from 24 to 6 sec intensified the disruptive effects of increasing RIs from 3 to 6 sec in the RIJITI lever-retracted group (Experiment 2), as would be predicted by the trial tracking hypothesis.