Indices of airflow resistance have been obtained in a group of 248 healthy London schoolchildren from recordings of peak expiratory flow rate (PEFR), forced expiratory volume in 0-75 seconds (FEV 0-75) and maximum mid-expiratory flow (MMEF) and two more direct methods, airways resistance (Raw) measured plethysmographyically and total respiratory resistance (PT) by the forced oscillation technique. The normal data are presented.