The heavy chain variable region composition of the human adult Ab repertoire is poorly defined, but recent evidence suggests that peripheral blood B cells may express a nonstochastic assortment of VH genes. In this study, the contribution of individual VH gene segments to the human Ab repertoire has been assessed. As a measure of VH gene utilization, the frequency of occurrence of eight individual VH3 gene segments contained in rearrangements was assessed in the peripheral blood B cells of two adult subjects. In addition, the frequency of occurrence of rearrangements containing nine individual VH4 gene segments was analyzed in one of the subjects. More than 2500 independent rearrangements were analyzed. For controls, amplifications and subsequent identification of nonrearranged VH3 and VH4 genes from the same individuals were also performed. The results of this germ-line analysis indicated that approximately 25 VH3 gene segments and nine VH4 gene segments could be amplified quantitatively. However, usage of elements was not uniform; one VH3 element, V3-23, and one VH4 element, V4-34, were represented among rearrangements more frequently than were other members of their respective families. This pattern of VH utilization was apparent in B cells isolated from the same subject after an 8-mo interval, indicating the relative stability of the repertoire over time. These results indicate that the adult human Ab repertoire is dominated by a few VH genes demonstrating a pattern of nonrandom utilization that could involve preferential rearrangement and/or receptor-dependent selection.