In this study, we analyze the human VH4 gene family and find it to exhibit a level of polymorphism similar to that of the much larger VH3 family. A cloned VH4 probe detected an average of 10 hybridizing BgIII restriction fragments in genomic DNA derived from 75 unrelated individuals and a total of 15 distinct bands. Of these 15 restriction fragments, 12 were polymorphic, as demonstrated by band absence in some individuals. Oligonucleotide probes specific to CDR1 and CDR2 sequences of known VH4 genes detected limited numbers of bands and revealed sequence polymorphisms that correlated with several of the RFLP detected by the cloned probe. The prevalence of the individual polymorphic restriction fragments was highly variable, ranging from 1% to 97%, with a mean prevalence of 51%. These values resemble those previously observed among VH3 elements. Analysis of linkage disequilibrium suggests that most VH4 gene segments are in genetic equilibrium. These results indicate that the VH4 loci, like those of VH3, are dominated by relatively few, perhaps two to four, alleles/locus and further suggest that the haplotype organization of the human VH locus is very complex.