Absence of disease or treatment that might provide a reasonable alternative explanation for the CD4 cell count or might confound the evaluation. Examples of such diseases would be any acute, severe medical illness that had not resolved when CD4 cell counts were obtained; active tuberculosis; leukemia or lymphoma; or previously characterized immunodeficiency disorder. Treatment that that might provide a reasonable alternative explanation includes chemotherapy over a field that could affect bone marrow or supraphysiologic glucocorticoid therapy.