Experimental conditions essential to a simple, reproducible, quantitative human immunodeficiency virus plasma assay were determined. Five parameters were evaluated: length of culture, reproducibility, assay dilution schema, washing procedures, and anticoagulant usage. The recommended quantitative plasma assay utilizes undiluted citrated plasma cultured with peripheral blood mononuclear cells for 14 days with fivefold dilutions and a medium change on day 1 with no washing.