When gastric cancer patients’ leucocytes were exposed to a panel of tumour extracts, leucocyte migration reactivity was ‘positive’ before operation (90% of cases), it declined after surgery and it reappeared in patients with local recurrence or metastases. In patients with non-malignant gastric diseases, ‘positive’ reactivity against tumour extracts was associated almost exclusively with atrophic gastritis with and without intestinal metaplasia (24/43 cases). ‘Positive’ patients also showed a pathological migration index with an extract of normal g