The organization and evolution of the 0.8-Mb JH-proximal region in the human Ig VH locus were studied by mapping DNA fragments hybridized to non-repetitive intergenic probes and by determination of the content and distribution of repetitive sequences. Southern blot analysis of cloned DNA covering the 0.8-Mb region with intergenic probes allowed us to map two to seven cross-hybridizing fragments by each probe. Clusters of fragments detected by an identical set of probes appeared repeatedly within the 0.8-Mb JH-proximal region. Distantly located VH segments flanked by a cluster of DNA fragments hybridized by the same set of probes were highly homologous to each other, providing evidence for recent frequent duplication and translocation throughout the locus. DNA fragments detected by the same set of probes were orientated with the same 5' to 3' order within the cluster, suggesting little involvement of inversion upon recombination in the locus. The content of interspersed Alu and L1 sequences in the VH locus were not significantly greater than the average in the genome.