The more expensive ARV drug is usually given to patients who are resistant to the cheaper version of anti-retroviral drugs.

The demonstrators said demands for co-payment had already killed many patients, who could not afford to pay such bills and were left to die.

"Some patients earn just Bt8,000 a month. How can they pay a bill totalling over Bt10,000 a month?" Aids Access Foundation manager Nimit Tien-udom said.

Another Aids activist, Supatra Nakapiew, said SSO should allow HIV-positive patients to live on. She said that with the demand for co-payment, many patients would not survive.

"The SSO should provide free blood tests for people covered under its health-benefit scheme if they suspect that they might have caught the virus," she said.

Free blood tests would help prevent Aids from spreading further, she explained.

SSO secretary general Surin Jirawisit met with the protest leaders. He said the SSO committee on medicine had already agreed to cancel the co-payment demand for patients with HIV.

"I also agree with the cancellation," he said. The SSO board was due to consider the proposed cancellation on Wednesday, and if the board gave it the green light, the issue would be forwarded to Labour Minister Apai Chandanachulaka.

"If things go as planned, the cancellation of co-payment should take effect on January 1," Surin said, adding he would try to push for it to have retroactive effect too.

Surin said there were about 23,000 HIV patients under the SSO health-benefit scheme and the SSO spent about Bt300 million a year to provide them with anti-retroviral drugs.

When the demand for co-payment is scrapped, the budget for such drugs should be raised to Bt400 million a year.

Surin said he agreed with the idea that the SSO provide free blood tests for people who feared they might have HIV.