Hemophilia is a recessive, hereditary disease linked to the X chromosome affecting primarily males, with the most common form being type A. The purpose of this investigation was to detect carriers related to hemophiliac patients identified in the northeastern part of Mexico. Twentyone families of hemophilic patients were studied, including a total of 60 women, 22 obligatory carriers (OC), and 38 possible carriers (PC). Results obtained in the quantification of factor VIII:C by a one-stage assay and of von Willebrand factor (FvW:Ag) by immunoelectrophoresis were compared with data obtained in a control group. The results were analyzed by discriminant analysis, linear regression, and the ratio, VIIIC/FvW:Ag, obtaining the following percentages of identification: 91% of OC and 66% of PC with discriminant analysis; 86% of OC and 27% of PC with linear regression, and 64% of OC and 18% of PC with the ratio. The control group was not positive for the test. The techniques used in this study were trustworthy, reproducible, and of low cost, so that procedures used in this investigation for the detection of hemophilia carriers may be implemented in a clinical laboratory as an alternative to the high cost of molecular studies. With a specificity of 91%, although these tests are inexpensive, they contain significant risk of misclassification from a genetic counseling standpoint. A negative result or a positive result with a positive family history would be useful. However, trying to identify a new mutation in a family with only a single affected son might be problematic. Am.