The problem that the proposal for recording the properties of putative taxa of procaryotes attempts to redress arises because the International Code of Nomenclature of Bacteria is not able to provide sensible regulation of nomenclature for new taxa defined by very limited data, such as a nucleotide sequence for a small portion of the genome. The constructors of the original code (1957) and the Judicial Commission considering the 1976 and 1990 revisions did not foresee or act upon the possibilities for molecular description and typification of procaryotes that were not yet cultivable. As a result, formal names are being proposed for uncultivated procaryotes whose uniqueness is defined only by very limited characteristics, such as differences in a molecular sequence. As the editors of two journals concerned with the systematics of procaryotes, we recognize that the problem will increase as the available technology gains wider use and becomes easier to apply. Accordingly, this note is presented in advance of discussions by the International Committee on Systematic Bacteriology at the forthcoming congress (July 1994) so that there may be discussions and reaction by colleagues.