Sir

Your Editorial 'The cost of silence?' (Nature 456, 545; 2008) questions our decision — as scientists who opposed dissident theories — to participate in the now-discredited AIDS advisory panel set up by former South African president Thabo Mbeki.

We had no role in, and did not see or approve, the panel's report (Nature 410, 730; 2001). Each of us had agreed independently to join the panel, guided by our consciences as scientists in a young democracy and without prior knowledge of who else had been invited to participate. To us, it provided an opportunity to present Mbeki with the alternative viewpoint and the compelling scientific evidence that HIV causes AIDS, in the hope that rationality would prevail.

However, Mbeki's antipathy to antiretroviral drugs was influenced by documents from and interactions with AIDS dissidents that predated the setting up of the panel. We underestimated the strength of his dissident views on AIDS and how little impact sound science would eventually make on them.

Sadly, our advice to Mbeki on AIDS causation and antiretroviral treatment was rejected. We cannot, therefore, be numbered among those held accountable for Mbeki's decisions, which led to the loss of many thousands of lives in South Africa through lack of access to antiretroviral therapy.

That we failed to change Mbeki's opinions on AIDS is a matter of record. But your Editorial is unreasonable in implying — with the benefit of hindsight — that scientists could have foreseen this failure and therefore should not have signed up to an opportunity to give the president critically important information that might have saved the lives of their fellow-countrymen.

We stand by our decision to participate in the Mbeki panel. We have an obligation to our country, which is suffering the worst AIDS epidemic in the world, to do everything in our power to provide our political decision-makers with the best scientific advice, whether or not they are a priori opposed to or supportive of our views.