Thirty-six infants and children presenting with recurrent respiratory disorders (RRD) as the sole clinical symptom including bronchial asthma (6), recurrent obstructive bronchitis with or without wheezing (18), chronic nocturnal cough (3), recurrent episodes of pneumonia (3), recurrent pharyngitis (3) and recurrent laryngitis (3) were investigated for associated gastro-oesophageal reflux (GER) by oesophagram, endoscopy and continuous 24 h pH monitoring of the distal oesophagus. The pH monitoring criteria were selected on the basis of a preliminary study comparing statistically measurements of 32 variables recorded in 15 patients who all had clinical, radiological and endoscopic evidence of GER and in 8 asymptomatic controls. Although patients with symptomatic GER differed significantly from the asymptomatic ones for 27 variables examined, 6 variables emerged as having the highest value for discrimination (overlap score 0-1). Among these, the Euler-Byrne index (number of reflux pH less than 4 + 4 times the number of reflux episodes of more than 5 min), the percentage of total reflux time and the number of reflux episodes 1 h post-cibal scored 0 (no overlap). GER was considered to be present when at least five of these six parameters were abnormal. The overall incidence of GER in children with RRD was 41% (15) when detected by oesophagram and 61% (22) when diagnosed by pH monitoring criteria. In the children with bronchial asthma or with recurrent laryngitis, the percentage of reflux time during sleep was about 40 times higher than in asymptomatic controls and 2 times higher than in those with symptomatic GER.(ABSTRACT TRUNCATED AT 250 WORDS)