The recent availability of small-volume spacers has facilitated the general use of inhaled treatment in infants. The purpose of this study was to evaluate any errors made by parents when using this new inhalation technique and the child's behavior during the inhalation. Ninety-four young children (61% boys) under 5 years of age were enrolled in the study. Inhalation treatment was recommended either by a general practitioner or by a pediatrician. Data concerning treatment regimens, the ability of parents to use the spacer and metered-dose inhalers (MDIs), and the acceptance of the devices, were collected by means of a demonstration and questionnaire. Unexpectedly, the doses, administration times, and duration of the treatments varied from one child to the next. No explanation or training in administering the treatment via the spacers was given to 12% and 47% of the parents, respectively. Fourteen per cent of parents did not shake the MDIs, 12% did not monitor the valves, and 22% allowed too short a time for inhalation. The lack of explanation increased the occurrence of errors in manipulation of the devices. The procedure was judged to be easy to follow by 78% of the parents, but the face mask was accepted with difficulty by 22% of the children. Repeated crying during administration of the treatment was observed in 38% of the patients, particularly the youngest. Crying influenced the acceptance of the face mask, reduced parental compliance, and made the use of the devices more difficult. Errors altering the efficiency of inhalation treatment in infants are frequent. Most of these errors could be avoided by spending more time to inform the parents about correct usage. Furthermore, repeated crying during inhalation is common in young children and this problem should to be taken into consideration in the evaluation of treatment.