The possible value of tidal flow volume (TFV) loops measured at birth in relation to the risk of developing recurrent or persistent bronchial obstruction within two years of life was assessed. TFV loops were measured at a mean age of 2.7 days in 802 neonates enrolled in the 'Environment and Childhood Asthma' (ECA) study in Oslo. Of these, 77 children developed recurrent or persistent bronchial obstruction (cases) and were included in a nested case-control study within the ECA study; 88 controls (the child born closest in time to the case), with no history of bronchial obstruction in the first two years of life, were also included. Information on socio-economic factors, parental atopic diseases and parental smoking habits during the pregnancy was collected from a questionnaire completed by the parents in the maternity ward, and cord blood IgE (CB-IgE) was determined as part of routine sampling in the delivery ward. Mean tPTEF/tE (time to reach peak flow to total expiratory time) was slightly lower in cases (0.31; 95% CI 0.28-0.34) than in controls (0.33; 0.31-0.35) (difference not significant), whereas geometric mean CB-IgE was significantly higher among cases (0.39; 0.30-0.52) than controls (0.27; 0.23-0.33). No significant differences between cases and controls were found for respiratory rate, peak tidal expiratory flow or expiratory volume. However, the odds ratio for developing recurrent or persistent bronchial obstruction was 3.5 (1.1-11.6) if tPTEF/tE was < 0.20 and 4.1 (1.1-14.5) with maternal daily smoking during the pregnancy, after adjusting for age, weight, sex, CB-IgE, parental atopy, maternal education and family income. The TFV parameter tpTEF/tE < 0.20 measured within the first week of life as well as maternal daily smoking during pregnancy are significant, independent risk factors for developing recurrent or persistent bronchial obstruction within the first two years of life.