Formalin-fixed and paraffin-embedded biopsy specimens from twenty-six patients with primary gastrointestinal lymphoma were evaluated by DNA flow cytometry. Nineteen of 26 samples (73%) had diploid DNA content and 7 (27%) had aneuploid DNA pattern. Proliferative (S phase) fraction in diploid samples ranged between 7-24.6% and the DNA index in aneuploid samples ranged between 1.3-2.3. Four of 10 low grade and 3 of 6 intermediate grade lymphomas had aneuploid DNA content, whereas none of the high grade lymphomas (0/10) had aneuploid DNA patterns (p < 0.05). The results suggest that aneuploidy may be a good prognostic indicator in primary gastrointestinal lymphoma.