In the paper by Chotai and Payne (J Med Genet 1998;35:472-475) on “A rapid, PCR based test for differential molecular diagnosis of Prader-Willi and Angelman syndromes”, the sequence of primer S2 (antisense) was wrong in two places. The correct sequence is as follows with the corrected letters in bold: 5′-CCCCTCCTCTACACAGCAATCAT-3′. The authors apologise to any readers who encountered difficulties in trying to amplify the above sequence.