During recent years there has been significant development of pulmonary function tests for use in preschool children. A range of tests including multiple inert gas washout, plethysmography, spirometry, interrupter resistance and impulse oscillometry have been shown to be feasible and to be able to identify diminished lung function in children with lung disease such as asthma or cystic fibrosis. An overview of these applications in clinical and epidemiological research is given. Future applications to investigate the longer term effect of preterm delivery, intra-uterine growth retardation, smoking and assessing the response to therapeutic intervention would strengthen the scientific basis for the prevention and treatment of respiratory disease in early life.