Serum alpha 1-antitrypsin (A1AT) allo- and phenotypes (including M1, M2 and M3 alleles) were studied in 99 patients with gastric ulcer (GU) and 56 patients with duodenal ulcer (DU) using agarose isoelectric focusing. The results were compared with the A1AT data of a random population sample of similar genetic background (1422 persons). An increase in M2 allotype and M1M2 phenotype as well as a decrease in Z allotype of A1AT was seen in GU in comparison to DU and the random population. There were no particular clinical features which would distinguish patients with M2 allotype from the remainder of the GU group. However, a trend toward elevated serum pepsinogen I and II levels in patients with M2 allotype was seen. When the pepsinogen levels were compared in the GU patient groups with and without M2 allotype, matched between themselves by the state of the gastric mucosa, a statistically significant difference was revealed between pepsinogen II levels in these two groups. No associations were found between DU and any of the A1AT phenotypes.