Summary The abundant synaptic protein, CaMKII, is necessary for long-term potentiation (LTP) and memory. However, whether CaMKII is required only during initial processes or whether it also mediates memory storage remains unclear. The most direct test of a storage role is the erasure test. In this test, a putative memory molecule is transiently inhibited after learning. The key prediction is that this should produce persistent memory erasure. We conducted this test using transient viral (HSV) expression of dominant-negative CaMKII-alpha (K42M) in the hippocampus. This produced persistent erasure of conditioned place avoidance. As an additional test, we found that expression of activated CaMKII (T286D/T305A/T306A) impaired place avoidance, a result not expected if a process other than CaMKII stores memory. Our behavioral results, taken together with prior experiments on LTP, strongly support a critical role of CaMKII in LTP maintenance and memory storage.