By generating new junctional fragments from the recombinant Charcot-Marie-Tooth (CMT) 1A-REPs in CMT1A patients, a 3.2-kb recombination hot spot is observed in three quarters of CMT1A patients. By a polymerase chain reaction (PCR) method the authors analyzed eight patients CMT1A duplication, confirmed by Southern blot, to detect a recombination hot spot. Four patients had a novel 3.2-kb junctional fragment by PCR analysis. These four patients with a novel 3.2-kb junctional fragment had an abnormal 1789-bp fragment in addition to 1986-bp fragment after NsiI digestion (type 1). One patient who demonstrated no novel 3.2-kb junctional fragment had an abnormal 336-bp fragment in addition to 265 bp (type 2). Three patients with CMT1A duplication were not diagnosed as having CMT1A on the basis of PCR analysis. The PCR-based DNA test is valuable for screening to detect CMT1A duplication.