The original reference to "Touchdown" PCR was Don, et al Nucleic Acids Res. 19, p. 4008 (1991). P. Flick -- Parke K. Flick, Ph.D. ch994 at cleveland.freenet.edu USB/Amersham Life Sciences, Inc. Cleveland, OH 44128 Ph: 216-464-9277; FAX: 216-360-0975