The experience with cytogenetic and flow cytometry methods used for the diagnosis of Fanconi anemia (FA) in one center is summarized. The tests consist of chromosomal breakage and cell cycle studied after sensitization by the introduction of nitrogen mustard into phytohemagglutinin-stimulated blood-cell cultures. The cytogenetic test was shown to be reliable in ascertaining the diagnosis of FA. Flow cytometry studies showed a marked increase in the percentage of cells in G2/M phase in FA patients after sensitization by nitrogen mustard. This increase, however, could not be detected in three FA patients with myelodysplasia or acute leukemia and the results were ambiguous on three occasions.