| By Peter Biles |
BBC News, Johannesburg
They follow newspaper allegations that she underwent a liver transplant while suffering from alcoholism.
The government says the reports are "false and speculative", and President Mbeki's office says he still has confidence in his health minister.
Dr Tshabalala-Msimang has - in the past - come under fire over her unorthodox approach to the HIV-Aids crisis.
Her emphasis on the use of garlic and beetroot for HIV sufferers brought her many critics.
But over the past fortnight, South Africa's Sunday Times newspaper has made startling allegations that the health minister was an alcoholic who jumped the queue to obtain a liver transplant earlier this year.
The paper has also said that as part of a five-month investigation, it discovered that Dr Tshabalala-Msimang was convicted of stealing from a patient when she worked as a medical superintendent at a hospital in Botswana 30 years ago.
The health ministry has dismissed the newspaper allegations as "false, speculative and bizarre".
It is now in the process of preparing a more detailed response.
President Thabo Mbeki's official spokesman, Mukoni Ratshitanga, has called on anyone with firm evidence, to produce it.
President Mbeki and Dr Tshabalala-Msimang have an association that stretches back more than four decades.
They were part of the same group of students which fled South Africa to go into exile in 1962.
Ten days ago, Mr Mbeki fired his deputy health minister, Nozizwe Madlala-Routledge, saying she had not been a team player and had made an unauthorised trip to an Aids conference in Spain.
Published: 2007/08/20 12:20:55 GMT
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