It was the first time such transplants have worked on primates suffering from the degenerative nerve disorder, said Nobuo Hashimoto, a doctor at the Department of Neurosurgery at Kyoto University Graduate School of Medicine.
"First, we have to confirm the effectiveness will last long," said Hashimoto on Tuesday, the chief researcher of the study.
"Once we can confirm the safety of the therapy, we want the method to be applied to humans," Hashimoto said. "We hope clinical applications on humans will be available in about five years."
"There are many approaches to curing the disease, such as strong drugs or destruction of troubled cells in the brain, but use of embryonic stem cells is seen as an ideal and fundamental therapy for the disease," he said.
The researchers extracted embryonic stem cells capable of releasing dopamine, a neurotransmitter, from fertilised eggs of cynomolgus monkeys.
It is a decline in production of dopamine that is believed to trigger Parkinson's disease, in which patients shake uncontrollably.
The embryonic stem cells were then transplanted into six cynomolgus monkeys, which had drug-induced symptoms similar to Parkinson's disease in humans.
"Once we can confirm the safety of the therapy, we want the method to be applied to humans"
Dr Nobuo Hashimoto,
Department of Neurosurgery, Kyoto University Graduate School of Medicine
Three months later, the monkeys' symptoms, such as trembling hands, had lessened, Hashimoto said.
Details of the experiment were published on the website of the Journal of Clinical Investigation on Tuesday.