February 19, 1969

Dr. Thomas H. kdC8S
Space Sciences Laboratory
Univerritp of C8llfornia
Barkeley, California 94720

Dear Torn:

Thank you for continuing to pram ma about DDT.

I am enclosing a letter that I mote recently to Senator Gaylord Welson,
whom I have some small persoual contact with from my Wisconsin days.  I
would urge you to  commun lcate directly with him on this subject, exprassing
the kinds of concerns that you raised in your letterr to me.

My general position is that any colnpound aa biologically effective as DDT
had better not be allowed to accumulate la the environment, which DDT does
appear to do 90 remarkably.  The pubHe health applicatfons of DDT are also
likely to be prejudiced by its indiscriminate use, which can only help to
accelerate the development of resistant variaties.

                         Sincerely yours,

Joshua Lederberg
Professor of Gcnettca