A cosmid clone containing the entire hCGβ gene cluster has been isolated. The restriction map of this clone has been determined by an indirect-end-label FIGE (field inversion gel electrophoresis) method. Analysis of this cosmid clone shows that there are 6 hCGβ genes in human genomic DNA. A previously uncloned portion of the hCGβ cluster, termed the "gap" region, has been shovn not to contain any sequences homologous to the hCGβ cDNA. The restriction mapping method employed in this study takes advantage of the superior resolution of FIGE for high molecular weight DNA fragments in the size range 15-50 kb. This method is broadly applicable and permits rapid and accurate restriction mapping for extended regions of genomic DNA that have been cloned into cosmid or lambda vectors. © 1987 IRL Press Limited.