18 February 1963
Dear Crick:
I am writing about the matter of the three hydrogen bonds between guanine and cytosine.  A man giving a seminar on the nucleic acids here a few days ago used the structure with two hydrogen bonds, and said that he supposed that you were still supporting it, as shown, for example, by your article in the Scientific American, which was published after the publication of the paper by Professor Corey and me, in which we pointed out that guanine and cytosine form three hydrogen bonds with one another.  He asked me if it did not seem, from your publications, that you and Watson had doubt about the third hydrogen bond.
I trust that you are going to introduce the third hydrogen bond in your published Nobel lecture.  I am writing just to be sure that, through oversight, you do not continue to refer to guanine and cytosine as forming two hydrogen bonds with one another.
Cordially yours,
Linus Pauling