The aim of the study was to investigate which features predict favourable response to omeprazole therapy in asthmatics with gastro-oesophageal reflux (GER). The study population consisted of 52 outpatient asthmatics with GER who had completed an intervention where they were randomized to receive omeprazole 40 mg once a day or placebo for 8 weeks. After a 2-week washout period the patients were crossed over. Asthma symptoms were found to be relieved > or = 20% in 18 (35%) patients who were thus regarded as responders. A logistic regression analysis was performed in order to identify which features separate the responders from the non-responders. More responders were found among the patients whose body mass index (BMI) was higher (P = 0.02) or whose distal esophageal reflux was more severe [total time (%) pH < 4 (P = 0.01) or time (%) pH < 4 in upright position (P = 0.04)]. Adding other predictors to the total time (%) pH < 4, which was the most significant predictor for response in multi-variate analysis, did not further increase the prediction for favourable outcome. It is concluded that severe distal oesophageal reflux and obesity predict amelioration in asthma symptoms after 8-week omeprazole treatment in asthmatics with GER. Adding more than one predictor does not seem to further increase prediction for favourable asthma response.