In 15 ill newborn infants a comparison between long-term multichannel and single-channel recordings of simultaneously tape-recorded (Medilog system) and amplitude-integrated EEG (Cerebral Function Monitor) was made. There was good agreement between the main type of background activity diagnosed with the tape-recorded and the amplitude-integrated EEG for all recordings. Two infants had repetitive subclinical and subtle seizure activity, lasting for several hours, which was detected by both techniques. Short, single seizures were diagnosed in the recordings of nine infants. When a single electrographic seizure appeared in an otherwise stable recording, it was identified by both the tape-recorded and the amplitude-integrated EEG. Very short (5-30 s) seizure patterns, which were diagnosed with the tape-recorded EEG, were not identified in the cerebral function monitor recordings. In the single-channel recordings of both the EEG and the cerebral function monitor there were, on some occasions, difficulties in distinguishing single seizures from interference due to external artefacts. In the multichannel recordings the diagnosis of seizure patterns was facilitated by comparison with the other channels. Both the Medilog EEG and the cerebral function monitor are feasible techniques for following cerebral electrical activity in sick neonates, although neither technique is specifically constructed for this purpose. For clinical use in the neonatal intensive care unit the advantage with the cerebral function monitor is the immediately available recording. The tape-recorded EEG offers possibilities of more channels and a higher reliability when diagnosing short subclinical seizures, however, only after offline analysis.