The role of subicular neurons is explored with respect to their participation in short-term memory during performance of a spatial Delayed-Nonmatch-to-Sample (DNMS) task by well-trained rats. Subicular and CA1 neuron firing was examined in the same animals in relation to the encoding of task-relevant events during the DNMS trial. The results indicate that subicular neurons have completely different firing signatures than well-characterized hippocampal neurons in this task. Firing patterns of subicular neurons consisted of five different categories spanning all three phases of the DNMS trial, but concentrated mostly within the Sample and early portion of the Delay period. Unlike hippocampal neurons, subicular cells did not exhibit conjunctive firing correlates with respect to particular combinations of task events; rather, subicular cell firing was differentiated primarily on the basis of temporal specificity within the trial. Only two of the five subicular cell types fired differentially on correct versus error trials; however, one cell type exhibited such differential firing as an inverse function of duration of delay interval. Experiments employing gamma-aminobutyric acid GABA(B) receptor agonists and antagonists showed that both behavioral performance as well as subicular cell firing were disrupted significantly by baclofen at short delays, while performance at long delays and hippocampal cell firing were relatively immune to this effect. The relevance of subicular cell firing in the task with respect to its temporal relation to delay-dependent hippocampal neuronal activity suggests that the structures have complementary roles in the encoding and representation of items in short-term memory.