Abstract Recent research on external-memory search has shown that disks can be effectively used as secondary storage when performing large breadthfirst searches. We introduce the Write-Minimizing Breadth-First Search (WMBFS) algorithm which is designed to minimize the number of writes performed in an external-memory BFS. WMBFS is also designed to store the results of the BFS for later use. We present the results of a BFS on a single-agent version of Chinese Checkers and the Rubik’s Cube edge cubes, state spaces with about 1 trillion states each. In evaluating against a comparable approach, WMBFS reduces the I/O for the Chinese Checkers domain by over an order of magnitude. In Rubik’s cube, in addition to reducing I/O, the search is also 3.5 times faster. Analysis of the results suggests the machine and state-space properties necessary for WMBFS to perform well.