Problems of nomenclature III: ambiguous abbreviations and catchwords.

To avoid ambiguity, the following emendations are advocated: (1) 2H, in place of H2, to designate the second histamine receptor; (2) HN-2, in place of HN2, to designate mechlorethamine (MBA);(3) 'pre-drug', in place of 'pro-drug', to describe molecular species which must undergo biotransormation before yielding an effective drug.