Gastroesophageal reflux disease accounts for approximately 75% of esophageal pathology. Accurate diagnosis can be complicated by the absence of endoscopic esophagitis in about 40% of patients with typical symptoms or atypical symptoms such as chest pain, chronic cough or wheezing. A number of tests have been developed to aid diagnosis, but 24-hour pH monitoring has emerged as the standard in reflux diagnostics. Although this method has been known for a long time, it has only become popular since small, portable digital recorders have been available. The aim of this retrospective study was to analyze our first experience with this method. Included in the study were the first 50 consecutive patients in our hospital who had undergone endoscopy of the upper GI tract followed by 24-hour pH monitoring. As a recorder we used the "GastrograpH-Fresenius Mark II". In agreement with the literature we considered the following findings as abnormal: esophageal acidity below pH 4 > 5% of total time or > 8% of upright time or > 3% of supine time, more than 4 reflux episodes of > 5 minutes, duration of the longest reflux episode more than 20 minutes. With this definition there were 24 patients (48%) with reflux disease. The reflux episodes chiefly occurred in daytime (68%), as known from the literature. The indications for this examination were chiefly given by pneumologists (50%), followed by gastroenterologists (22%) and cardiologists (14%). Acid block therapy was performed in 83%, with success in 42% and failure in 8%. In 50% of the patients the necessary data were lacking. Based on these results we conclude that 24-hour pH monitoring has shown itself reliable for the diagnosis of reflux disease and should always be performed in patients with negative endoscopic examination but typical or atypical symptoms of gastroesophageal reflux.