We demonstrate that transfer of a yeast artificial chromosome (YAC) containing 230 kb of the human beta-globin locus into mouse erythroleukemia cells by fusion results in correct developmental regulation of the human beta-like globin genes. Additionally, we show that early after hybrid formation, human embryonic epsilon- and fetal gamma-globin genes are coexpressed with the adult beta gene but that after 10-20 weeks in culture, globin gene expression switches to predominantly adult. Thus, in contrast to shorter gene constructs, the globin genes of the beta-globin locus YAC are regulated like the chromosomal globin genes. These results indicate that transfer of YACs into established cell lines can be used for the analysis of the developmental control of multigenic and developmentally regulated human loci.