incurable. back in the mid-1980s, i had reported on the work of a young stanford neurologist named bill langston, who had come across something startling that seemed to cause parkinson's. now, more than 20 years later, i've headed back to bill langston's parkinson's institute. since the 1980s, langston and his team have pursued whether environmental toxins might trigger the disease, a quest quest that began with a most unusual patient. >> it really started with my getting called to see a patient who had developed parkinson's literally over two or three days. and he was young; that's not typical. it came on quickly; that's not typical. so he was a true medical mystery. >> can you raise this hand up at all? can you raise that hand up? >> he was literally frozen like a statue. >> i can see you trying. >> so i knew instantly we had a neurologic condition on our hands, but what? we had no idea. >> narrator: what langston and his team were about to discover would turn the parkinson's...