Exchange of Correspondence Regarding the Original Experiments on AZT

March–April, 1999
David Crowe, Richard Beltz

David’s Original Letter

Dear Richard:

I am writing on the off chance that you are one of the researchers who worked on the development of the anti-cancer (and now AIDS) drug Azidothymidine (AZT). A person with your name was quoted as saying:
“AZT was shelved for two reasons: My studies showed that it caused cancer at any dose and it was too toxic even for short term use.”
If you are the AZT researcher in question, can you confirm that you made this statement?


David R. Crowe
Alberta Reappraising AIDS Society

Richard Beltz’s Reply

Date: Wed, 14 Apr 1999 15:15:04 -0700
From: "Richard Beltz" <>
X-Accept-Language: en
Subject: AZT and AIDS

Dear President Crowe:

I synthesized AZT in my laboratory as a NIH Senior Research Fellow (National Cancer Institute) in the autumn of 1961. The AZT was among a group of four thymidine analogs that I prepared at that time. AZT proved to be the most biologically active of these compounds. My biological tests showed (1) AZT inhibited the growth of E. coli and Salmonella potsdam at very low concentrations, and (2) cultures of E coli put on agar plates containing AZT showed AZT-resistant clones after a few days of incubation. Subcultures of these clones were completely resistant to growth inhibition by AZT. Further work showed that AZT had no effect on the DNA synthesis of T2 bacteriophage propagated in E. coli cultures. Finally, I prepared 1 gram of crystalline AZT and sent it to my friend Dr. Alan Sartorelli, Professor of Pharmacology at Yale University, for testing against animal cancers. It proved to be completely inactive in all of the test systems he employed. In my laboratory I found AZT incapable of inhibiting the growth of Jensen sarcoma cells in vitro at very high concentrations. Thus, AZT showed no activity as a potential anticancer drug at that time. What I have written here summarizes my work with AZT. I did many other experiments within the framework of these findings, but it consisted of filling in the details.

Now let me say that I am aware of the existence of certain quotes attributed to me on the Internet, such as the one you mentioned in your letter. Such quotes are completely untrue! Never at any time did I study the potential of AZT to cause cancer, nor did I investigate the toxicity of AZT in animals or humans. At that time I was interested in AZT as a potential anticancer drug. When AZT proved to be inactive in the experimental tumor systems that I and Sartorelli tested it against, I discontinued my work on AZT. It seemed possible to me, then, that AZT was a cure looking for a disease, but what disease? [AIDS didn't emerge until around 1980, as you know.]

I regret very much being wrongly quoted on the Internet in regard to AZT. I am sorry if such quotes have led to incorrect conclusions about AZT, which we must admit has at least some limited value as an anti-AIDS drug, especially for preventing newborn children from AIDS-infected mothers from acquiring the disease.

Sincerely yours,

Richard E. Beltz, Ph.D.
Professor of Biochemistry
School of Medicine
Loma Linda University,
Loma Linda, CA 92350

Copyright © David Crowe, Friday, May 14, 2004.