During the early experience with omeprazole, it was recommended that plasma gastrin levels be monitored to identify patients with 4-5-fold increases above baseline. Such patients were thought to be at an increased risk of developing gastric carcinoid tumours. Studies have established that plasma gastrin levels usually rise 2^1-fold during omeprazole therapy, there being considerable inter- and intra-individual variation. Approximately 3.3% of patients have plasma gastrin levels above 400 pg/ml when treated continuously for 1 year. In clinical practice, it is not cost-effective to screen all patients to detect such a small percentage, particularly given the paucity of realistic treatment options in such patients, and the growing evidence that hypergastrinaemia during omeprazole treatment is of little, if any, clinical significance.