[en] Radioimmunoassays (RIA) were used to measure plasma apo A-I and apo E levels using polyclonal antibodies. Purified human apoproteins were used as the primary standards and labeled antigens. A quality control sample (pooled plasma from 8-10 subjects) was used as a secondary standard. Fasting plasma was obtained from 16 normal subjects and stored at -70⁰C in small aliquots. The intra- and interassay variations were estimated by measuring 16 subjects repeatedly for 11 times (for apo A-I) or 4 times (for apo E) over a period of 4 months. In each experiment, 9 replicates (3 replicates/dilution; 3 dilutions/plasma sample) were run on each subject; whereas, 27 replicates (27 replicates/9 dilutions) were run for the quality control samples. The intra-assay variation was 7% for apo A-I and 12% for apo E. The interassay variation was 13% for apo A-I and 19% for apo E when calibrated only against the primary standard. However, the interassay variation was reduced to 5% for apo A-I and 8% for apo E when calibrated against both the primary standard (purified apo A-I or apo E) and the secondary standard (plasma quality control sample)