Dr Wakefield stands by his findings
The doctor who first suggested a link between MMR and autism paid children £5 for their blood samples at his son's birthday party, a hearing was told.
Dr Andrew Wakefield and two colleagues face professional misconduct charges over their controversial research into the measles, mumps and rubella vaccine.
The General Medical Council alleges the trio acted unethically and dishonestly towards the Lancet medical journal.
They all deny the allegations in the case which could last several months.
The case centres on research carried out by Dr Wakefield, and colleagues Professor John Walker-Smith, and Professor Simon Murch, which raised doubts about the safety of the triple vaccine.
The suggestion of the 1998 research paper - published in the Lancet - was that MMR was linked not only to autism, but also to the bowel disorder Crohn's disease.
It led to falling numbers of parents immunising their children and a row over whether the then prime minister, Tony Blair, had vaccinated his son, Leo.
But the medical establishment has repeatedly argued that the triple vaccine is perfectly safe.
And a host of major studies has since failed to find any evidence of a link between MMR and autism.
The allegations against the doctors relate to investigations for their study on 12 youngsters with bowel disorders carried out between 1996 and 1998.
At the time, all three doctors were employed at the Royal Free Hospital's medical school in London, with honorary clinical contracts at the Royal Free Hospital.
It was also alleged that 11 children were subjected to a series of invasive tests, including colonoscopies, lumbar punctures, blood and urine tests and MRI scans.
This was contrary to their best clinical interests and Dr Wakefield did not have the "requisite paediatric qualifications" nor sought the right approval for the tests, the charge sheet went on.
Dr Wakefield and Prof Walker-Smith are also accused of acting "dishonestly and irresponsibly" in failing to disclose in the Lancet paper the method by which they recruited patients for inclusion in the study.
And it is alleged that a drug was administered to one child for experimental reasons.
The allegations that he took blood from children at his son's birthday party date back to prior to 20 March 1999.
Later on, he joked about the incident while giving a presentation at the Mind Institute in California, and said he intended to get samples the same way in the future, the hearing was told.
Another of the key allegations against Dr Wakefield is that he was being paid at the time for advising solicitors on legal action by parents who believed their children had been harmed by MMR.
All three doctors are accused of conducting the study on a basis which was not approved by the hospital's ethics committee.
One example is that some of the children may not have qualified for the study on the basis of their behavioural symptoms.
In a statement ahead of the hearing Dr Wakefield's solicitor said: "Dr Wakefield continues to vigorously deny any allegation of wrongdoing."
The Lancet has disowned Dr Wakefield's 1998 paper, the editor admitting he would not have published it if he had known about what he called a "fatal conflict of interest".
The campaign group, Jabs, which believes MMR has damaged children, has been demonstrating in support of Dr Wakefield outside the GMC.