Objectives: Children with peripheral airways obstruction suffer the negative effects of intrinsic positive end-expiratory pressure: increased work of breathing and difficulty triggering assisted ventilatory support. We examined whether external positive end-expiratory pressure to offset intrinsic positive end-expiratory pressure decreases work of breathing in children with peripheral airways obstruction. The change in work of breathing with incremental pressure support was also tested. Design and setting: Prospective clinical trial in a pediatric intensive care unit. Patients: Eleven mechanically ventilated, spontaneously breathing children with peripheral airways obstruction. Interventions: Work of breathing (using pressure-rate product as a surrogate) was measured in three tiers: (a) Increasing pressure support over zero end-expiratory pressure. (b) Increasing applied positive end-expiratory pressure and fixed pressure support. The level of applied positive end-expiratory pressure at which pressure-rate product was least determined the compensatory positive end-expiratory pressure. (c) Increasing pressure support over compensatory (fixed) positive end-expiratory pressure. Measurements and results: Increases in pressure support alone decreased pressure-rate product from mean 724 +/- 311 to 403 +/- 192 cmH(2)O/min. Applied positive end-expiratory pressure alone decreased pressure-rate product from mean 608 +/- 301 to 250 +/- 169 cmH(2)O/min. The lowest pressure-rate product (136 +/- 128 cmH(2)O/min) was achieved using compensatory positive end-expiratory pressure (12 +/- 4 cmH(2)O) with pressure support 16 cmH(2)O. Conclusions: For children with peripheral airways obstruction who require assisted ventilation, work of breathing during spontaneous breaths is decreased by the application of either compensatory positive end-expiratory pressure or pressure support.