In this report, we first present MultiCode PLx testing data on a variety of genomic DNAs with various genotypes prepared from several sample types for the presence or absence of mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Finally, data are presented on a prospective study comparing testing results obtained for freshly prepared blood spots by the PLx assay and the commercially available CF Gold Linear Array TM system (Roche Molecular). ) . DNA was extracted from whole blood and dried blood spots on Guthrie cards. The dried blood spots were stored at room temperature for 2-3 days after receipt until routine testing was completed. For long-term storage, dried blood spots were stored at 4°C. DNA extraction from Guthrie cards was performed with the Generation Capture Card Kit (Gentra Systems) according to the manufacturer's guidelines for DNA purification and elution. DNA was extracted from whole blood by use of the Puregene DNA Isolation Kit (Gentra Systems) or the Whatman FTA system (Whatman Inc., Clifton, NJ). All genomic DNAs from these preparations were diluted 1:10 in water, and 1L was added to each PCR reaction (1-50 ng of total DNA). As a cross-reference and in the prospective study, genotypes were also determined by CF Gold linear array or DNA sequencing if discrepancies were detected.