Long-term memory in Drosophila is separable into two components: consolidated, anesthesia-resistant memory and long-lasting, protein-synthesis-dependent memory. The Drosophila memory mutant radish is specifically deficient in anesthesia-resistant memory and so represents the only molecular avenue to understanding this memory component. Here, we have identified the radish gene by positional cloning and comparative sequencing, finding a mutant stop codon in gene CG15720 from the Drosophila Genome Project. Induction of a wild-type CG15720 transgene in adult flies acutely rescues the mutant's memory defect. The phospholipase A2 gene, previously identified as radish [Chiang et al. (2004) Curr. Biol. 14:263-272], maps 95 kb outside the behaviorally determined deletion interval and is unlikely to be radish. The Radish protein is highly expressed in the mushroom bodies, centers of olfactory memory. It encodes a protein with 23 predicted cyclic-AMP-dependent protein kinase (PKA) phosphorylation sequences. The Radish protein has recently been reported to bind to Rac1 [Formstecher et al. (2005) Genome Res. 15:376-384], a small GTPase that regulates cytoskeletal rearrangement and influences neuronal and synaptic morphology.