We have used synthetic oligonucleotides corresponding to human V(H) sequences to analyze sequence variation in human genomic DNA. By using probes 20 to 24 bp long and conditions of hybridization and washing under which identity in 17 to 21 consecutive bp is required for hybridization, it has been possible to dramatically reduce the complexity of hybridization patterns. We have been able to identify unambiguously individual V(H) elements. Concomitant with the reduction in ovrall complexity of hybridization patterns has been a marked increase in the variation between hybridization patterns when different individuals are compared. Variation between individuals was detected using probes corresponding to both framework and complementarity determining regions and depended in part on the complexity of the corresponding V(H) gene family. Probes corresponding to a cDNA clone belonging to the single-member V(H)6 family, hybridized to a single, invariant, band in all individuals tested. An oligonucleotide probe corresponding to CDR2 of one member of the V(H)3 family also detected a single, invariant, band in all individuals tested. However, an oligonucleotide probe corresponding to framework region 2 revealed variants of more than 40% of the 22 V(H) elements it detects. In addition, a panel of 5 oligonucleotide probes corresponding to a second member of the V(H)3 family revealed variants of 10 of 14 elements detected. The patterns of variation suggest that some V(H) elements have multiple alleles, whereas some elements are remarkably conserved. The number of variant elements we have detected is evidence that the haplotype arrangement of the human V(H) locus is probably extremely complex. Importantly, this heterogeneity may contribute directly to disease susceptibility in man.