The effect of the new histamine H2-receptor antagonist ramixotidine 750 mg p.o., administered at 22.00 h, on intragastric and intraoesophageal pH monitored from 22.00 h to 08.00 h, was studied in a double-blind cross-over trial in 11 duodenal ulcer patients. Placebo and ramixotidine were given to each patient on 2 consecutive days in a randomized sequence. Three patients were excluded from the intragastric pH analysis as the records on the second study day were technically inadequate. No significant carry-over or sequence effect was noted. Intragastric hydrogen ion activity was significantly lower (p = 0.01) after ramixotidine than after placebo: median (range) 24 (9-100) vs 97 (27-188) mmol/l. The percentage of time with intraoesophageal pH less than 4 was less than 5% in all but three recordings, with a maximum value of 12%, and it was not significantly different after the two treatments.