A special video camera devised by the author and a fiberscope were used to film the neonatal sucking response of 50 low-risk full-term newborn infants on the 5th day after birth. Analysis of the sucking behaviour showed that the sucking movements consist mainly of a peristaltic tongue movement and two kinds of negative pressure; that the peristaltic tongue movements are synchronized with the jaw movements; that infants actively adapt to a varying environment; and that the sucking movements change to minimize the energy required.