By Zoë Corbyn

Controversial researcher Peter Duesberg has been cleared of wrongdoing following formal complaints made after he and others published a paper arguing that there is "as yet no proof that HIV causes AIDS."

Duesberg, who is well known for denying the link between HIV and AIDS, escaped censure from the University of California, Berkeley, after an investigation upheld his academic freedom and found no clear evidence that he broke faculty rules in publishing the paper.

A letter dated May 28 from Sheldon Zedeck, vice-provost for academic affairs and faculty welfare, to Duesberg effectively clears him of any wrongdoing. It states that there was "insufficient evidence" available to pursue any disciplinary action against him, although it stresses that the investigation was not concerned with the "accuracy or validity of the article."

Duesberg told Nature that he felt "officially exonerated" by the outcome but was disappointed that Berkeley had not dismissed the allegations sooner. "There was no basis for a misconduct charge," he says.

The professor of biochemistry and molecular biology, who won international acclaim for his work on cancer genes in the 1970s before focusing on AIDS, says that his detractors will now find it more difficult to make a case against him. "Now they will have to find something else ... maybe my parking permits," he suggests.

Contentious hypothesis

Berkeley launched an investigation last November, questioning whether Duesberg had violated the university's code of conduct when submitting an article to the journal Medical Hypotheses, which at the time did not peer review its papers.

The article argued that there is "as yet no proof that HIV causes AIDS" and described claims that the virus had killed millions as "unconfirmed." Duesberg had previously submitted the manuscript to the Journal of Acquired Immune Deficiency Syndromes, where one reviewer warned that he could face misconduct charges were the paper to be published.

The warning concerned the alleged cherry picking of results and the failure to declare a conflict of interest for co-author David Rasnick, previously an employee of Matthias Rath. Rath sells vitamin pills as remedies for AIDS. Rasnick has denied any conflict of interest and says that he has had no connection with Rath since 2006.

The paper's publication led to a storm of protest from scientists, and retrospective peer review later led to its being permanently withdrawn. The journal's editor was sacked and publisher Elsevier vowed to make changes to Medical Hypotheses, including introducing peer review.

Two formal complaints were also lodged with Berkeley, between them alleging that Duesberg had made false claims in the paper and accusing him of failing to declare Rasnick's alleged conflict of interest. One complaint came from Nathan Geffen, treasurer of the South Africa-based Treatment Action Campaign--which campaigns for the rights of people with HIV/AIDS. The other complainant has remained anonymous.

Geffen told Nature that he submitted his complaint because he believed Duesberg had behaved unethically. "I would like them to have taken action against him but I understand their position. I am willing to accept that this is a grey area in terms of their code," he says.

He adds that having "insufficient evidence" to proceed is not the same as exoneration. "This is anything but an exoneration."

Berkeley spokesman Robert Sanders confirmed that the investigation into Duesberg had now concluded.

"Academic freedom protects a professor's right to engage in scholarly research, even if it is controversial. The university relies on the scholarly peer-review process, rather than disciplinary procedures, for evaluating the value of scientific work," he says.