Autophosphorylation of α-Ca2+/calmodulin kinase II (αCaMKII) at Thr286 is thought to be a general effector mechanism for sustaining transcription-independent long-term potentiation (LTP) at pathways where LTP is NMDA receptor-dependent. We have compared LTP at two such hippocampal pathways in mutant mice with a disabling point mutation at the Thr286 autophosphorylation site. We find that autophosphorylation of αCaMKII is essential for induction of LTP at Schaffer commissural–CA1 synapses in vivo, but is not required for LTP that can be sustained over days at medial perforant path–granule cell synapses in awake mice. At these latter synapses LTP is supported by cyclic AMP-dependent signalling in the absence of αCaMKII signalling. Thus, the autophosphorylation of αCaMKII is not a general requirement for NMDA receptor-dependent LTP in the adult mouse.