In a pilot study at the Frenchay Hospital in Bristol, southwestern England, the drug called GDNF helped five patients move better and, for one sufferer, restored the sense of smell and the ability to laugh.
"We thought that this drug would take some months or even years to be effective. We found that within a month or two patients were noticing significant changes in their ability to do things," Dr Steven Gill, the neurosurgeon who led the study, told BBC radio.
GDNF, which stands for glial derived neurotrophic factor, is a natural growth agent needed by brain cells to produce dopamine, which is necessary to transmit impulses or messages to the body. A reduced concentration of dopamine in the brain is associated with Parkinson's disease.
Gill stressed that the results, which were presented at a meeting in Denver of the American Academy of Neurology, are preliminary and it is still unknown how long the improvements will last or whether the treatment is suitable for all Parkinson's patients.
It is the first time such improvements have been shown in patients following infusion with a growth factor. But Gill and his team said further trials are needed to confirm the drug's efficacy and safety.
Parkinson's is an incurable neuro-degenerative disease. It affects 120,000 people in Britain and millions more around the world including the actor Michael J Fox and boxing legend Mohammed Ali.
Patients suffer tremors in the limbs, poor balance and have difficulty speaking and initiating movements. Treatment with the drug levodopa can restore normal movement in patients with early disease but it gradually loses effectiveness.
If the treatment is proven safe and successful, it could become widely available but that would not happen for at least four to five years.
"We are greatly encouraged by these early results of what is a three-year study," Robert Meadowncroft, of the Parkinson's Disease Society, said in a telephone interview.
In other studies, GDNF has been shown to block the degeneration of nerve cells in animals bred to develop Parkinson's disease.
The protein has also shown promise as part of a gene therapy treatment for the illness. When scientists inserted the gene for GDNF inside a harmless virus and injected it into the brains of monkeys it made the dopamine producing cells work better.
By Patricia Reaney
By Patricia Reaney