We examined the contribution of physiologic and environmental variables to the process of weaning a child with chronic respiratory failure from mechanical ventilation support. Surveillance measures, e.g., blood oxygenation, were obtained from a 6-year-old child with multiple medical and developmental disorders who received three different rates (24, 22, and 20 tidal volumes per minute) of intermittent mechanical ventilation. Direct observations were used to calculate rates of aberrant behavior, e.g., aggression toward self, for task versus play settings within the intermittent mechanical ventilation rates. Rates of aberrant behavior and adult responses were tabulated from videotaped observations for task, attention, and no attention settings. The greatest rate of aberrant behavior occurred during tasks compared with play activities, regardless of whether attention was provided while playing. Adults also responded more often to aberrant behaviors during task versus play conditions. Clinical implications are discussed concerning the inclusion of developmental and behavioral variables during weaning from mechanical ventilation.