Pulse cytophotometric analysis of bone marrow cells from 175 patients with leukemia or lymphoma showed abnormalities of cellular DNA distribution in 29 patients for an overall incidence of 16.6 percent. Comparative standard cytogenetic examination indicated that high-degree chromosomal aberrations (less than or equal to 44, greater than or equal to 53 chromosomes) can generally be detected on DNA histograms, whereas patients with diploid, pseudodiploid, 45-hypodiploid, and 47-hyperdiploid abnormalities usually escape recognition by this technique. There were 11 patients with normal diploid or near-diploid karyotypes exhibiting marked DNA deviations; this discrepancy may reflect lack of proliferation of some leukemic clones which is a prerequisite for cytogenetic identification.