The aldolase B gene was mapped to chromosome 9 using a rapid gene mapping system. This system uses a dual-laser sorter to identify and separate metaphase human chromosomes stained with either DIPI-chromomycin or Hoechst-chromomycin. Chromosome panels were constructed from a normal cell line by sorting 22 chromosome fractions directly onto nitrocellulose filters. Twelve labeled gene probes hybridized to the sorted chromosomal DNA fractions predicted by previous chromosome assignments. Eighteen newly cloned genes have been mapped using the same protocol.