The recent discovery that the gene causing Huntington's disease (HD) resides on chromosome 4 has generated increased interest in this autosome. Chromosome 4 contains two of the more informative conventional genetic markers, GC and MNS, but most loci have been assigned to it by recombinant DNA techniques. There are currently more anonymous DNA fragments detecting restriction fragment length polymorphisms (RFLPs) on chromosome 4 than on any other autosome. In addition, most of the cloned genes from this chromosome detect useful RFLPs. A genetic linkage map including both conventional and DNA markers should soon span the entire chromosome and will undoubtedly lead to the localisation of other inherited disorders.