Specifications for the AMPLICOR HIV-1 MONITOR kit indicate that the results are invalid if the optical densities (ODs) from the PCR-amplified sample that are between 0.1 and 2.3 units are out of sequence. However, among 11,904 assays, results were biased only when ODs of 0.2 to 2.0 units were out of sequence, reducing the rate of invalid results from 3.2 to 0.59%.