Evaluation of serum alpha 1-antitrypsin levels in the South Asian population and its possible involvement in disease conditions such as duodenal ulcer has not been given due consideration. This is mainly because reports from European and North American countries indicate that the genetic deficiency of this protease inhibitor is rare among Asians of the subcontinent. Using isoelectric focusing (IEF) and radial immunodiffusion (RID) techniques, we analysed serum samples from 100 normal, healthy adults and 50 patients with endoscopically proven duodenal ulcers to determine if there is a possible relationship between alpha 1-antitrypsin phenotype and this disease. Five duodenal ulcer patients had low alpha 1-antitrypsin levels as well as SZ and S phenotype. None of the controls showed presence of S or SZ phenotypes. The normal or most common genetic form, MM, is the predominant phenotype in both controls and patients.