Twenty-four infants were ventilated through a series of rates (30, 60 and 120/min), to determine which rate was most successful in provoking synchronous respiration. Their spontaneous respiratory rate was also documented during a temporary disconnection from the ventilator: respiratory rate and gestational age were significantly correlated (r = -0.85). Seventeen infants showed synchronous respiration at a ventilator rate of 120/min and 4 at 60/min. Of the remaining 3 infants, 2 only showed synchrony if ventilated at their own spontaneous respiratory frequency (between 60-75/min) and 1 infant was asynchronous at all rates including her own spontaneous respiratory frequency. The 17 infants synchronous at a ventilator rate of 120/min were significantly less mature (p less than 0.01) and had a faster spontaneous respiratory rate (p less than 0.01) than the 6 infants synchronous at ventilator rates of 60-75/min.