In contrast to the previous report, we conclude that N-acylaminoacyl residues do not transfer stereoselectively in either nicked-loop or nicked-duplex scenarios. Due to the lack of experimental detail reported by Tamura et al. , it is difficult to see where our conflicting results originate. It is possible that the different sequences used demonstrate different levels of selectivity, something we have seen in some exceptional cases with the transfer of aminoacyl residues in a nicked loop. Alternatively, simple experimental errors in the previous work such as differing loading onto gels (no loading control is shown) or significantly hydrolysed mixed anhydride starting material synthesised from D-AcAla, are potential causes.