Objective To explore the clinical validity of the new Access® pregnancy-associated plasma protein-A (PAPP-A) assay for Down's syndrome screening. Setting Academic hospital. Method Residual serum samples ( n = 416) received for routine first trimester Down's syndrome screening (10-13 weeks) were retrieved from freezer storage and tested using two PAPP-A immunoassay methods. The new Access® assay was specifically compared, on a subset of these samples ( n = 194), with an assay proven to give acceptable Down's syndrome screening performance, the PerkinElmer (PE) AutoDELFIA method. Access® PAPP-A levels were examined in relation to gestational age and maternal weight, and were compared with the PE method by regression and Bland-Altman analyses. Results Access® PAPP-A assay results were highly correlated with the PE AutoDELFIA method ( r = 0.97). PAPP-A levels obtained using the Access® assay increased with advancing gestational age and were inversely related to maternal weight, as expected. The distribution of multiples of the median (MoM) values fit a log Gaussian distribution and the standard deviation of the log MoM (0.2331) matched published estimates. PAPP-A MoM levels in Down's syndrome pregnancies ( n = 6, median 0.30) showed the expected reduction. Conclusion Using an appropriate gestational age-specific median equation, the Access® PAPP-A assay is expected to perform acceptably in first trimester Down's syndrome screening.