A DMSO-enhanced LiOAc transformation protocol was described in NAR (1991). 19,5791. They reported that they could use competent cells after they were frozen in 5% DMSO. I find that it works quite well in my hands, however, as they indicated, the efficiency is only in the 10e4 range. Mike Kladde PennState Univ. 308 Althouse Lab. University Park, PA 16802