Maribeth had thirty million fetal pig cells implanted into the part of her brain damaged by the stroke. Since the operation, Maribeth has completed a half-marathon, although she still uses a leg brace to walk. Each month her blood is drawn and sent to the Centers for Disease Control for testing, a process which she must follow for the rest of her life. But according to Maribeth's husband: "It's just amazing to see the condition she's in today -- mentally and physically, since this pig cell transplant. Overall, her spirits are just better. Maribeth's thought processes are much clearer,...Her speech has significantly improved since this operation."

Although her case is an experimental success, Maribeth was part of the early, Phase 1 clinical trial by the biotech company Diacrin to see if xenotransplants of pig cells can help stroke victims.

Read more about this clinical trial and the outcomes for all five patients involved.

But her gamble involves a risk beyond her own. She could become infected with pig virus, which, if it spread to others could become a major public health risik. Her doctors recommended she not have children because the long-term effects are still unknown. In addition, she signed a remarkable medical research consent form that will govern the rest of her life: no blood donations, safe sex and recording of her partners. She also has had to agree to follow up for life and access to her tissues after her death for research studies.

A week after the procedure, Amanda had a seizure and further clinical trials were halted while the doctors investigated why. In the ten months that have passed since the treatment, Amanda has had no new seizures and can walk easily without her brace.

The early Phase 1 clinical trial in which both Amanda and Maribeth Cook took part is still on hold.

Read more about the outcomes of this initial clinical trial.

In 1997 he became part of an experimental Phase I clinical trial by Diacrin/Genzyme. Jim was one of the first people to have millions of fetal pig neural cells injected into part of his brain. The results were dramatic. Six months later, he could walk independently and get up and sit down from a chair. His neurologist, Dr. Samuel Ellias, said: "It's very unusual to see this level of improvement in someone who's already been on most of the treatments for Parkinson's disease which have begun to fail, and are not working well. His gains have been really remarkable." Jim Finn is now a Patient Advocate and voting member of the Secretary's Advisory Committee on Xenotransplantation (SACX) which operates under the auspices of the National Institutes of Health (NIH).

Read more about Diacrin/Genzyme's subsequent Phase 2 controlled trial for Parkinson's patients and the set back that has been indicated by early data from this trial. Also, explore Jim Finn's diary chronicling his experience as a xenotransplantation recipient.

For seven hours over three days, Robert was attached to a pig liver from a transgenic pig developed by biotech company Nextran. Then, a human liver became available. This procedure was done just weeks before such experiments were halted by the FDA because of fears of a pig virus spreading to humans. According to Dr. Marlon Levy, Robert's transplant surgeon, "Robert has done well. The other patient that we have experimented with in this way has also done well. Their family members continue to be alive and well. Our staff doesn't seem to have been infected with any unknown or strange disease."

But the risk from the pig virus remains; live cells from the pig liver were undoubtedly flushed into his body during this procedure and they may survive in his body. So far, his blood has tested negative for unusual infections.

Pennington was one of a half dozen patients on a Phase 1 clinical trial whose lives were saved using pig livers.

Read more about this clinical trial and Nextran's interest in future clinical trials for pig to human transplants.