A noninvasive scintigraphic technique was used to estimate enterogastric reflux and subsequent gastric evacuation of refluxate in 35 normal, healthy subjects and 55 patients previously treated by vagotomy or partial gastrectomy. Reflux was provoked by a milk drink and quantitated by counting 99Tcm-EHIDA activity within the gastric area during gamma camera imaging. Seven normal subjects (20%) showed reflux of 5-18% of initial activity (mean: 10%), with peak values occurring at 5-30 minutes (mean: 14 minutes) following the milk. Gastric evacuation of activity in these subjects was monoexponential (r = 0.993, T1/2 = 24.1 minutes). Reflux occurred more frequently than normal in patients with truncal vagotomy and drainage (22/28 patients) and partial gastrectomy (20/21 patients). All of 16 patients with Billroth II anastomoses exhibited reflux, which was excessive compared with refluxing normal subjects (mean: 25%; p less than 0.01) and occurred later into the study (mean: 34 minutes; p less than 0.01). Ten of 11 asymptomatic patients showed reflux of similar amounts of activity (mean: 21%) compared with 16 patients who complained of bile vomiting (mean: 22%). However, asymptomatic patients exhibited gastric evacuation of refluxate at a rate similar to that of refluxing normal subjects, while bile vomiters showed significant gastric retention of refluxate at 25-30 minutes following peak gastric activity (p less than 0.05). This result confirms that post-operative bile vomiting is essentially a problem of gastric emptying.