I would like to return to the main theme of this meeting and ask the theoretical chemists who are here whether they think that the degrees of specificity that have been mentioned during the meeting can be explained by specific binding in terms of the kinds of intermolecular forces discussed yesterday by Professor Buckingham, or whether in certain cases it is necessary to postulate something beyond specific binding. I have in mind Dr Blow’s question yesterday, when he referred to the small effect on binding that would be expected to result from the absence of a methyl group, and the point that Dr Dalziel made today about the failure of NADP dehydrogenases to work with NAD, which differs only by the absence of a phosphate group.