We have calculated normal standards for lung function of Australian children and have estimated the effects on lung function of passive smoking, current asthma, past asthma, and a current respiratory infection. Three cross-sectional samples of children in school years 3-5 (aged 8-11 years) were studied. The 2765 children were from two rural regions of NSW and from the city of Sydney. Details of passive smoking and respiratory illness were collected by a questionnaire sent to parents. Forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1), peak expiratory flow rate (PEFR), and forced mid-expiratory flow rate (FEF25-75%) were used as measures of lung function. Airway responsiveness was assessed by histamine inhalation test. Data from 1278 "normal" children were used in regression analysis to calculate prediction models for lung function. Passive smoking was associated with reduced FEV1, PEFR, and FEF25-75%. Children with current asthma had reduced FEV1 and FEF25-75% and children with past asthma had reduced FEF25-75%. Children with a current respiratory infection had reduced FVC, FEV1, PEFR, and FEF25-75%. The effects of these deficits on the future lung function of these children is not known but is likely to be important.