AIMS: An increase in the proliferative state of the gastric epithelium has been attributed to infection with Helicobacter pylori. In order to obtain a more precise estimate of the magnitude of this change, the proliferative state of 17 cases of florid H pylori associated follicular gastritis was examined using the antibody MIB-1. METHODS: Comparable results were produced from control and gastritis cases by using a combination of two reproducible measures of the labelled cells. Dividing cells in the gastric mucosa are concentrated within a proliferating compartment, situated at the base of the crypts. This compartment was measured and expressed as a proportion of the total crypt length. The proportion of positively labelled cells within the compartment was also counted. RESULTS: The proliferation compartment in the gastritis cases occupied 45.6% of the gastric crypt compared with 15.4% in the control group. Of the cells in the proliferating compartment, 79.5% were positively labelled in the gastritis cases and 33.4% in the control group. CONCLUSIONS: The convoluted nature of the gastric crypt does not make it a forgiving experimental model. The use of long lengths of mucosa obtained from gastrectomy specimens permitted the production of consistent results, using a morphometric method. The greater than 100% difference in the proportion of proliferating cells between the two groups suggests that further investigation is warranted.