Since 1975 four-channel ambulatory monitoring has been available as a technique for prolonged EEG recording in an unrestricted environment. This increases EEG sampling time so that attacks can be recorded and enables the differentiation of epileptic and non-epileptic attacks. In recent years an eight-channel system has become available which provides greater scalp coverage and allows better localization of attacks and EEG abnormalities. Four-channel recording has been widely used to assess the efficacy of anticonvulsant medication in patients with absence seizures. It has also been used to investigate the effect of the environment on discharges, as well as any circadian variations in discharges. Ambulatory monitoring provides a useful alternative to sleep recording in the laboratory, both for the detection of abnormalities during sleep and for experimental sleep studies. Automated analysis techniques have so far been confined to the analysis of spike and wave activity and to the scoring of sleep stages.