Mobilized blood CD34+ cells from cancer patients were ex vivo infected by a recombinant adenovirus vector carrying an alkaline phosphatase gene, whose expression is evaluable by flow cytometry. A mean of 40% CD34+ cells were infected by the vector, with high levels of expression of the transgene. Among attempts to improve infection efficiency by manipulating culture conditions, only reinfection by the same vector achieved a 10% increase of transgene expression. Transduced CD34+ cells were induced to differentiate along the myeloid and the dendritic lineage, and in either case AP+ cells were detectable among the differentiated cell population. We conclude that adenovirus vectors may be useful tools for gene transduction into mobilized blood CD34+ cells, particularly for those applications in which high transgene expression for limited periods of time is required.