With the use of the forced oscillation technique, respiratory input impedance was measured in 371 healthy children, aged 5-12 years. How impedance values varied with height (age) and gender and to what extent negative frequency dependence of oscillatory resistance existed in these children was investigated. Negative frequency dependence of resistance between 8 and 28 Hz was a common finding in all height categories. With increasing height, resistance decreased and reactance increased in all children. Below 140 cm of height, resistance values at 8 Hz were higher, and reactance values at 8 Hz were more negative in girls than in boys. At heights above 140 cm the reverse was found. Resonant frequency was found to be higher in boys than in girls. The incidence of negative frequency dependence of resistance (FD) decreases during growth. Over heights of 130-160 cm, more negative FD existed in boys than in girls. It can be concluded that negative FD between 8 and 28 Hz can be found in healthy children up to 12 years of age, most pronounced in boys, not necessarily implicating pulmonary pathology.