Serum levels of alpha-1-antitrypsin (alpha 1-AT) were measured and phenotypes were determined in 47 patients with cancer of the pancreas and in 160 hospital controls. The mean value of alpha 1-AT (+/- SEM) in cases with cancer of the pancreas was 486 (+/- 18) mg/100 ml, and it was significantly higher than the corresponding mean value in controls, which was 434 (+/- 13) mg/100 ml (p approximately 0.02). The frequency distribution of the cases of pancreatic cancer by alpha 1-AT phenotype was: M1M1 49%, M1M3 21% and other phenotypes 30%, whereas the corresponding frequency distribution among controls was: M1M1 53%, M1M3 21% and other phenotypes 26%; the two distributions are clearly compatible (p greater than 0.50).