Another reader has brought to our attention a fourth paper showing that GSM radiation can alter sleep. James Horne and coworkers at the Sleep Research Centre at Loughborough University in the U.K. have reported that very weak (0.133 W/Kg) signals can delay sleep onset. The new work, published in June, raises some particularly important —and thorny— issues regarding the biological effects of different ELF modulations on the 900 MHz GSM pulses. We'll leave those for another time, but for now the Loughborough study reinforces the take-home message that RF effects on sleep have become a major focus of the mobile phone health controversy.