Synapse-Associated Protein 102 (SAP102/Dlg3) and PSD-95/SAP90/Dlg4 belong to the Membrane-Associated Guanylate Kinase (MAGUK) family. They contain protein-protein interaction domains & bind directly to NMDA receptors (NMDAR). PSD-95 mutants are profoundly disturbed in cell signalling, LTP & spatial behaviour (Migaud et al, 1998). Mutations in the human SAP102/Dlg3 gene result in X-linked mental retardation (Tarpey et al, 2005). To examine the role of SAP102 in vivo, mice were created with a targeted knockout mutation (Cuthbert et al, SfN 2005). Here we report the behavioral characterisation of these mice in a battery designed to assess aspects of learning & memory (L&M). During acquisition of the water maze task (5d), the mutants had similar escape latencies to controls, but were swimming faster over longer distances but no differences in 2 probe tests. During reversal training (5d), no differences in escapes to the new platform were seen, but in daily probe trials, the mutants took longer than controls to...