Reference equations which express indices obtained from forced expiratory maneuvers in relation to height and/or other independent variables are lacking for infants and children with artificial airways. The present study was performed to establish normative data of forced expiration by forced deflation in healthy intubated and paralyzed infants and children and to develop prediction equations in relation to height and to ulna length to enable pulmonary assessments in children whose height is difficult to measure. Measurements of forced and passive expiratory maneuvers after inflation to +40 cmH₂O inspiratory pressure were prospectively obtained in 100 healthy, anesthetized children from 0 to 5 years of age. Linear regressions of log-transformed FVC, MEF₂₅, and MEF₁₀ obtained by forced deflation (-40 cmH₂O airway opening pressure) and of analogous indices obtained by passive deflation were used to develop prediction equations from height or ulna length. FVC was significantly dependent upon age and height or ulna length. Prediction equations for FVC using height or ulna length were as follows: ln (FVC in ml) = - 5.6 + 2.8 x ln(height in cm) and ln(FVC in ml) = 0.46 + 2.5 x ln(ulna length in cm). Younger subjects had a significantly steeper slope for FVC versus height than the older age group. Normal reference data for forced expiratory maneuvers in intubated infants and children up to 5 years of age will enable improved assessment of pulmonary dysfunction in acutely or chronically ventilator dependent in children. Using ulna length instead of height should facilitate respiratory assessment in ventilated children with spinal or joint deformities