Although it sounds like it might be a myth, such as the old, erroneous belief that tomatoes can be a deadly poison, food scientists confirm that green potatoes are dangerous. They contain high levels of solanine, a toxin that can cause nausea, headaches and neurological problems.
All potatoes produce small amounts of solanine as a form of natural insecticide. But potatoes that undergo prolonged exposure to light and warm temperatures can produce unusually high amounts of solanine. The green color is caused by similarly high levels of chlorophyll, which is produced at the same time. A person weighing 100 pounds would have to eat about 16 ounces of green potato -- about one large baked potato -- to get sick.
The New York Times July 3, 2007