Total NK cells counts in AIDS-RL with <300 CD4+ lymphocytes/mm3 and HIV + patients without lymphoma but with <300 CD4+ lymphocytes/mm3 were lower than in the other groups (mean 41 ± 35/mm3 for AIDS-RL <300 CD4+ lymphocytes/mm3 and 51 ± 52/mm3 for HIV + without lymphoma with <300 CD4+ lymphocytes/mm3vs 137 ± 257/mm3 for AIDS-RL with >300 CD4+ lymphocytes/mm3, 131 ± 148/mm3 for HIV + with >300 CD4+ lymphocytes/mm3, 276 ± 510/mm3 for HIV-negative lymphoma patients and 150 ± 70/mm3 for HS (p = 0.04 and 0.02). The gene discussed is CD4; the disease is histiocytic sarcoma.