To assess functional cortical organization in newborns during quiet sleep we investigated instantaneous interhemispheric coherences in six healthy full-term subjects using linked ear reference and average reference. Tracé alternant was the most frequent EEG pattern during quiet sleep of these newborns and consists of burst and interburst periods. The calculation of coherence was performed by means of time-variant autoregressive models on the basis of Kalman filtering. Coherence changes simultaneously with the appearance of these burst and interburst periods. The highest level of coherence was observed during burst periods in comparison with interburst periods. The lowest level of coherence was observed just before the burst started. During burst, maximal coherence was reached at different moments--late in the low frequency band (0.5-1.5 Hz; about 3 s after the burst started) and earlier in higher frequency bands (> 2 Hz, about 2 s). Interhemispheric coherence depended on the region being investigated. A significant level of coherence could be observed over frontal, temporal and occipital regions. Our data demonstrate significant modification of interhemispheric coherence during quiet sleep of full-term newborns and, irrespective of the immaturity of the brain, these coherences differ significantly between cortical regions.