OBJECTIVE To examine the in vivo properties of retroviral recombinants carrying partially deleted human beta-globin gene (delta beta) and truncated erythroid enhancer (292 bp and 341 bp of 5'HS2) at the mRNA levels following short- and long-term reconstitution in mice with infected marrow cells. METHODS First ecotropic virus producer cell lines with higher virus titers were isolated using "ping-pong" procedures. Then the human beta-globin gene was transferred into murine hematopoietic progenitor cells and the integration and expression of transferred gene were analyzed by southern blot and RNase protection assay or RT-PCR. RESULTS The virus titers of both recombinants increased obviously after "ping-pong" procedures. The transferred human beta-globin gene was detected in murine CFU-S12 and the expression level was about 0.5%-5% of endogenous mouse alpha-globin gene. In 3 of 14 mice surviving long-term transplanted with bone marrow cells transduced with high-titer virus, bone marrow, spleen and thymus from two mice and bone marrow and spleen from another mouse contained the intact proviral genome. Long-term expression of the transferred gene was seen in one mouse at level of 7% of endogenous murine alpha-globin gene. CONCLUSIONS The transferred human beta-globin gene can stably integrate into murine hematopoietic stem cells mediated by retroviral vectors and express in an erythroid-specific manner.