In this study 55 adult volunteers (mean age 30.7 years) were exposed or sham-exposed to Rf radiation on two successive weekends. The exposure order was random. The 30 minutes exposure using a GSM 895 MHz including 217 Hz pulse modulation. The signal was of 0.25 W average power and the average SAR value measured over 10 g of tissue was 0.674 W/kg. The experimenter and the subject were blind to the exposure condition. Participants were instructed not to pass urine after 20.00 hours. They were started on their 30-minute exposure about 22.00 hours, and gave a urine sample at the end of the exposure and at 06.00 hours the next morning. The concentration of 6-sulphatoxymelatonin (6-OHMS) in the urine was determined.

6-OHMS output was determined in two ways. The total amounts were calculated by 6-OHMS concentration x urine volume collected. The other method was to use the ratio of 6-OHMS concentration to creatinine concentration. With the first method, there was no difference in 6-OHMS output in pre- or post- bedtime measurements between the RF- and sham-exposed states. With the 6-OHMS to creatinine ratio, the pre-bedtime output was significantly less for the RF-exposed group. This was entirely due to 4 individuals who had outputs that were extreme "outliers" compared to the others. It was thought that this was due to this small group having delayed onset of melatonin production, or some confounding factor e.g. prior exposure to bright light before coming to the laboratory.