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Mobile phones present the strongest source of radiofrequency electromagnetic held exposure to the human head. Mobile phones are routinely assessed with respect to safety by specihc absorption rate measurements at maximum output power. The difference of the exposure due to power control during normal usage was evaluated. A mobile measurement system to assess the effect of the power control in real networks was developed. It presents a realistic load to the phone and is able to measure the output power and band synchronously for the GSM900, DCS1800, and UMTS1950 bands. The system has a dynamic range of 60 dB and a measurement uncertainty of <;1 dB for GSM and <;1.5 dB for UMTS. Using the system, three mobile phones were evaluated in the three Swiss networks in urban and rural areas. The phones were tested in dual system (GSM and UMTS) and GSM only modes. The results show a small change of the mean output power in GSM mode (from -2 to -10 dB) compared to 30-dB power control dynamic range. The mean output power in UMTS was a factor >100 lower than GSM. In urban areas, UMTS was generally available and preferably used by the phones with rare fall backs to GSM. In the suburban/rural area, UMTS was hardly available or used by the phones.