The effects of radiofrequency field (RF) on self-reported symptoms and detection of fields after a prolonged exposure time and with a well-defined group of subjects including those reporting symptoms attributed to mobile phone use was studied. The design was a double-blind, cross-over provocation study testing a 3-h long GSM handset exposure versus sham. The study group consisted of 71 subjects aged 18-45, including 38 subjects reporting headache or vertigo in relation to mobile phone use (symptom group) and 33 non-symptomatic subjects. Subjects reported their belief of actual exposure status. The results showed that headache was more commonly reported after RF exposure than sham, mainly due to an increase in the non-symptomatic group. Neither group could detect RF exposure better than by chance.