Patients infected with the human immunodeficiency virus are at increased risk for developing intermediate-grade and high-grade B-cell lymphomas that in many instances contain Epstein-Barr viral (EBV) DNA. Because interleukin-5 (IL-5), a potent stimulator of eosinophil growth and differentiation, has been detected recently in EBV-infected B-cells, we hypothesized that some acquired immunodeficiency syndrome-related lymphomas with EBV DNA also might contain eosinophilia and IL-5. After reviewing files entered into our archives during the past 3 years, we identified four cases of human immunodeficiency virus-associated, high-grade, B-cell lymphomas that also contained extensive infiltration by eosinophils. Cryopreserved DNA from two of these four cases was available for amplification by the polymerase chain reaction, and both cases yielded an easily identifiable, EBV-specific amplification product. From one of these cases we also were able to extract mRNA and perform messenger amplification phenotyping (MAPPING) for the detection of mRNA coding for IL-5. After reverse transcription of mRNA from this case to cDNA and amplification by the polymerase chain reaction, we identified an amplification product that co-migrated with IL-5-positive controls in an agarose gel. We conclude that some AIDS-related lymphomas are associated with eosinophilia and that the eosinophilia may be related to EBV infection and transcriptional activation of the IL-5 gene.