Eyewitnesses report having caught a glimpse of a bear on Monday night in the Alps near the Swiss border with northern Italy, where a corridor of land was set aside earlier this year to encourage an existing population to spread north.
Officials in the eastern Ofenpass National Park were still searching yesterday for crucial evidence, such as droppings, tracks or hair, that could confirm the sighting.
Three nature-lovers claim to have seen the bear from a distance of 600 metres with binoculars. They say the animal emerged from a wooded area into an open meadow, where they were able to watch it for 20 minutes. The light was too weak to photograph it.
If their sighting proves to be correct - and conservationists, who have been waiting for the return for the past six months, say the testimony is credible - the comeback would be a boon for Switzerland.
The Government is keen to attract the species back to its mountains and has created three corridors of land linking the eastern Swiss hills with the Trentino region of Italy, between 24 and 54 miles away.
This week's sighting suggests that at least one bear has made the journey across the border in search of fresh hunting ground.
If its presence is confirmed, the lone creature should be able to acclimatise well to its new surroundings, according to the Swiss-based Worldwide Fund for Nature. It is thought that brown bears, once widespread in Europe but now endangered due to loss of habitat, would have no difficulty adapting to the undulating Swiss countryside.
But whether or not they are welcomed by the farming population, already battling other newly returned predators, is another matter. A recently re-established lynx population in the Bernese Oberland has led to a fall in the numbers of local sheep and cattle, while mystery still clouds the fate of a wolf which wandered into Switzerland from France several years ago and was found to have died inexplicably, or was killed, in the countryside.
But the re-appearance of the brown bear should in general be cause for rejoicing. The animals have, after all, always been the mascots of the capital, Berne, where they have decorated the canton's flag and coat of arms and have been kept as popular public attractions since 1480.
The relationship between the city and its ursine inhabitants has, however, always been fraught. Berne may well be named after the German word Bären, meaning "bears", but the reason for the christening bestows rather less honour on the animals than might be initially thought. Legend has it that a bear was the first unlucky animal to be killed during a hunt when the city was founded in 1191, and that the ruling duke, Berthold V, simply wanted to set the historic bloodshed in stone.