Medtronic Inc. (MDT) and Eli Lilly & Co. (LLY) agreed to collaborate on an early stage research project for a potential Parkinson's disease treatment that involves delivering medication directly to the brain.

The pact adds to Medtronic's roster of projects aimed at using implantable drug pumps and catheters to circumvent the blood-brain barrier. The tightly packed network of cells in brain capillaries only lets certain substances through, such as key nutrients, making brain-based disorders an elusive target for drug makers.

Medtronic, the largest stand-alone medical-device maker, already has a handful of other Parkinson's collaborations underway. The company is also working through home-grown efforts and collaborations on potential treatments for other brain diseases, such as Alzheimer's and Huntington's.

The latest effort with Lilly is still many years from yielding a marketable treatment or even starting human testing, so it remains to be seen whether it will become a major contributor for either company. The companies didn't disclose terms of their agreement, but a Medtronic spokesman said it spans early research through product development and potential commercialization.

Parkinson's is a progressive, degenerative brain disorder that affects nearly 1 million Americans, according to the Parkinson's Disease Foundation, and can lead to tremors and other movement problems. The disease, which has no cure, is thought to be caused by the death of neurons that produce the important chemical messenger dopamine. Lilly's treatment approach involves a modified form of a protein called "glial cell derived neurotrophic factor," or GDNF, which is designed to protect these neurons.

Seven years ago, Amgen Inc. (AMGN) stopped studying a potential GDNF Parkinson's treatment delivered with Medtronic equipment because it didn't appear effective. But Lilly hopes its compound, together with Medtronic's modernized delivery system, will "overcome some prior technical hurdles," said Ros Smith, senior research director of regenerative biology at Lilly. The company believes its GDNF variant has potential to have broader distribution in the brain than prior versions.

The drug may not enter human clinical trials for up to five years, Smith said.

Medtronic's system involves small catheters that are implanted in the brain and connected to a hockey puck-sized pump, which would likely be implanted in the abdomen. At this point it isn't known whether the treatment would involve short- or long-term infusion, or what specific areas of the brain might be targeted, said Steve Oesterle, senior vice president of medicine and technology at Medtronic.

The company already has experience finding and delivering treatment to parts of the brain responsible for Parkinson's through its "deep-brain stimulation" business, which makes pacemaker-like implants that deliver electrical stimulation through electrodes. That approach is used to treat Parkinson's symptoms, however, while drug approaches from Lilly and other companies have potential to restore damaged parts of the brain, Oesterle said.

The key is getting the drugs on site, rather than having them circulate through the body but get stymied by the blood-brain barrier. Medtronic has previously disclosed partnerships with small drug developers Neurologix Inc. (NRGX) and privately held NeuroNova AB of Sweden on potential Parkinson's treatment.

-By Jon Kamp, Dow Jones Newswires; 617-654-6728; jon.kamp@dowjones.com

--Peter Loftus and Matt Jarzemsky contributed to this article.