STOCKHOLM — The use of mobile phones over a long period of time can raise the risk of brain tumors, according to a Swedish study released on Friday, contradicting the conclusions of other researchers.

Last year, the Dutch Health Council, in an overview of research from around the world, found no evidence that radiation from mobile phones and TV towers was harmful.

Results released in January from a four-year British survey also showed no link between regular, long-term use of cell phones and the most common type of tumor.

But researchers at the Swedish National Institute for Working Life looked at mobile phone use of 2,200 cancer patients and an equal number of healthy control cases.

Of the cancer patients, aged between 20 and 80, 905 had a malignant brain tumor and about a tenth of them were also heavy users of mobile phones.

"Of these 905 cases, 85 were so-called high users of mobile phones, that is they began early to use mobile and/or wireless telephones and used them a lot," said the authors of the study in a statement issued by the Institute.

Published in the International Archives of Occupational and Environmental Health, the study defines heavy use as 2,000 plus hours, which "corresponds to 10 years' use in the work place for one hour per day."

Early use was defined as having begun to use a mobile phone before the age of 20.

There was also shown to be a marked increase in the risk of tumor on the side of the head where the telephone was generally used, said the study, which took into account factors such as smoking habits, working history and exposure to other agents.