In an antigen-capture RT-PCR study, a cDNA-RNA technique yielded an estimate of 79 HAV particles:PFU; the estimated limit of detection was 0.053 PFU, the equivalent of four particles (Deng et al. 1994) . These degenerate ratios are more likely the result of inefficiency in the initiation of infection at the cell level than of a large proportion of defective or noninfectious virions.