A pair of studies reach different conclusions on whether cell phones pose health risks to consumers, continuing a trend of conflicting scientific results that keeps consumers scratching their heads and plaintiffs' lawyers filing lawsuits.

One study, published in the British Medical Journal earlier this year, failed to link cancer with mobile-phone use of up to 10 years. Researchers said additional research was needed to study longer latency periods to see if brain tumors develop in adults. A study to be published shortly will address just that.

"Overall, we found no raised risk of glioma associated with regular mobile-phone use and no association with time since first use, lifetime years of use, cumulative hours of use or number of calls," the BMJ study stated.

The second study, set to appear in the February issue of the International Journal of Oncology, found a significant increase in the risk of benign tumors--particularly acoustic neuromas--from long-term cell-phone use. The pooled analysis of two case-control studies focused on the relationship between cell-phone use and the risk of benign tumors diagnosed between 1997 and 2003. The study discovered the risk was particularly high for people first exposed to cell phone radiation before the age 20. Teens are a major target market for the wireless industry.

But the IJO study is bound to raise eyebrows and suspicion within the industry because it was headed by Dr. Lennart Hardell, a Swedish epidemiologist whose expert testimony for a plaintiff in an $800 million brain, cancer lawsuit against Motorola Inc. and others was found lacking by a federal judge in 2002.

Government health and safety agencies in the United States and abroad say research showing no association between cell phones and cancer outnumber studies that have found cell phone radiation causes genetic damage and other biological effects. Courts have upheld Federal Communications Commission guidelines limiting the level of radio-frequency radiation that can be emitted by cell phones.

For those and other reasons, government health officials have chosen neither to order recalls on cell phones nor warn consumers to limit their wireless minutes--unlike a leading British authority, which did just that several years ago. But many of the same government officials refuse to guarantee the safety of cell phones, and they say additional research is necessary to address inconsistencies in research and uncertainties regarding long-term use.

While studies on the topic are inconclusive, there has been a resurgence of litigation in the arena. Some suits have faced jurisdictional rulings, while others seek to force carriers to supply consumers with headsets to reduce their exposure to cell phone radiation.

Although the cell phone industry has yet to get tagged in a health suit, wireless carriers and manufacturers have lost legal ground on jurisdiction.

Five headset cases remain alive--four have returned to state courts--after a conservative federal appeals court in Richmond, Va., in 2004 overturned U.S. District Judge Catherine Blake's 2003 dismissal of the class action suits.

Industry strongly urged the Supreme Court to review the Fourth Circuit's decision, but the high court last year let the lower court ruling stand.

While several health-related suits are pending in Blake's Maryland court, mobile-phone companies are closely watching arguably the biggest legal threat to them today. The Superior Court for the District of Columbia is getting closer to deciding whether to keep or throw out six brain-cancer lawsuits against wireless carriers, wireless manufacturers, trade associations and industry standards bodies. The wireless industry's motion to dismiss the brain cancer suits was filed more than a year ago.

The cell phone industry faces a challenge in arguing the suits should be rejected on federal preemption grounds in view of recent court decisions.