The objective of this study was to quantify the degree of disagreement in interpretation of spirometries and in the definition of the airway obstruction and response to bronchodilators (Bd) in different publications. Two surveys were carried out in which two groups of 15 pulmonologists were asked to identify in several spirometries the presence and degree of obstructive or restrictive defects (OD or RD), the response to Bd and whether the test was assessable or not. Three "problem' spirograms (PS) were included. For RD there was 76.1% of maximum agreement (MA). For OD the MA was 63.6%. Of the PS only 14% of the tests with a higher than 40% variation among the curves, 14% of those which did not include the graphic records and 33% of those with a considerably imperfect curve were considered nonassessable. The degree of disagreement for response to Bd was 24% (this implies 53.3% of possible maximal disagreement). Besides, every original article whose title or summary referred to "asthma', "chronic obstructive lung disease' or "chronic airflow obstruction' which was published from July 1991 to July 1993 in two respiratory medical journals (Chest and Thorax) was examined. Eleven different criteria to define obstruction were found. The most frequently used was FEV1/FVC < 70% (33.3%). Five different definitions of a positive response to Bd were found. The most popular was an increase in FEV1 > 15% of the initial value (76%). We conclude that there is very often disagreement in the interpretation of conventional spirometry. The definition of obstruction and reversibility in clinical trials is not uniform and great care must be taken when extrapolating the results from one publication to another since the composition of its samples could be substantially different.