Like prisoners emerging from a lifetime behind bars, a group of chimpanzees step blinking into the sunlight with what appears for all the world to be a wave and a smile.

And they have much to be joyful about. For this is the first time they have felt grass under their feet and breathed fresh air for 30 years.

Though a few of the chimps were born in captivity, most were kidnapped from African jungles as babies and flown to Europe, where they were locked in metal laboratory cages to be used in a long series of experiments.