April 26, 1948.
Dr, .obert Guthrie,
National Institute of Health,
Bethesda 14, wJjarylanl.
Dear Guthrie,

If I am not Mistaken, ATCC 9723 is the strain which Koepke, Lampen, ete.
uged in their exreriments, ksn't it? I haven't been able to find evidence
of reccoubination between mutants of this strain, so I have no inmediate
interest in them. As to 5& mutants, I have had in mind using «iditional
matunts .s genetic markers, but have no present need for them. Sinse, aa
T underatand it,you are in touoh with Tatua [ shan't bother to ask for
the straina you offered at this time; bd and 4 are reguiariy exchanging
cultures. 7

I hope ycu will have an opportunity to visit our laboxatory, sihce
it is rather unlikely that we shall be golng te Minneapolis. Please
give our regards to Howard vason, whe told us (Esther and ms) that he
spends mueh of his time discussing your work with you.

Yours sincerely,

Joshua Lederberg. -