Individuals infected with HIV (Human Immunodeficiency Virus) frequently develop B cell non-Hodgkins lymphoma. Although previous studies have failed to document the presence of HIV sequences in these tumors, the recent demonstration of malignant transformation of primary B lymphocytes by HIV-1 has prompted us to reinvestigate this issue. We have examined DNA extracted from 7 lymphomas and 5 lymphadenopathy specimens for HIV LTR (long terminal repeat), gag, and tat sequences using the polymerase chain reaction (PCR). All samples produced products of the expected size with primers for these regions, indicating the presence of HIV proviral sequences in these tissues. The amount of provirus in the tissue was estimated by normalizing the amount of HIV product to the amount of product for the cellular myc gene or beta globin gene. Products were quantitated during the exponential phase of DNA accumulation. These studies indicated that provirus was present at approximately one copy per cell in the 7 lymphoma samples and in 4 of the 5 lymphadenopathy samples. These results are consistent with a direct role for virus in the initiation of lymphoma. Studies to determine whether provirus resides in the lymphoma cells per se will be necessary to further substantiate this hypothesis.