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%. Comparative standard cytogenetic examination indicated that high-degree chromosomal aberrations (≤44, ≥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.