PCR for the neo gene in bnx/hu bone marrow and tissues. DNA was extracted from the bone marrow and tissues of each long-term engrafted mouse, and subjected to PCR to detect the presence of the neo gene, to determine whether or not gene marking of long-lived human hematopoietic cells had occurred in human hematopoietic progenitors or their differentiated progeny residing within each organ. Hybridization with a neo-specific oligonucleotide probe was done to ensure that the product band had been correctly amplified. Tissues that were positive and negative for the presence of the neo gene were amplified as controls in each reaction. The results from one set of mice are shown.