To investigate changes of intracerebral blood flow velocity correlated to different behavioural states, pulsed Doppler measurements were performed on anterior cerebral artery in 12 preterm and term neonates under polygraphic recordings and in view of the infants' behavioural state. Under very strict definition of the behavioural states there were significant differences in the parameters Vm (+25%), Vd (+75%), and Vs (+11%) in active compared to quiet sleep state. MABP was not significantly different in all examined behavioural states. From our results we conclude that in further Doppler studies the infants' behavioural state at the time of measurement should be assessed carefully.