Deficiency of alpha1-antitrypsin (AAT) is a common but underdiagnosed genetic disorder. Severe AAT deficiency may be detected by the absence of alpha1-globulin protein fraction by serum protein electrophoresis (SPEP). Routine SPEP may represent an underused resource for the identification of AAT deficiency. Total alpha1-globulin protein was measured in 47 MM, 24 MZ, and 19 ZZ phenotype serum samples by a Sebia CAPILLARYS (Norcross, GA) capillary electrophoresis system. Measured serum AAT concentrations by immunoassay exhibited moderate correlation with measured SPEP alpha1-globulin fraction concentrations. In this sample set, 16 (84%) of the ZZ, 7 (29%) of the MZ, and none of the MM sample phenotypes exhibited alpha1-globulin concentrations of less than 0.21 g/dL. From estimates of MZ and ZZ phenotype prevalence, it can be calculated that 1 ZZ phenotype should be present in approximately every 31 samples with alpha1-globulin concentrations of less than 0.21 g/dL. Clinicians should consider investigation of potential AAT deficiency in patients who exhibit low alpha1-globulin protein levels by routine SPEP.