We present a new, simple, and inexpensive sandwich-type double-antibody enzyme immunoassay for alpha 1-antitrypsin in dried blood collected on the fifth day post-partum. The method is very sensitive, having a detection limit of 2.84 fmol/well. Intra- and interassay CVs are 6.1% and 10.3%, respectively, for assay of 5-mm-diameter blood spots eluted into 7 mL of phosphate buffer. Since February 1984, we have used this method to systematically screen 39 289 consecutive births: 336 of these newborns (0.085%) showed values for alpha 1-antitrypsin below the cutoff value of 800 mg/L (50th percentile, 1470 mg/L). Of these 336 we were able to obtain 0.5 mL of serum from 161 for further testing. Four presented with a ZZ phenotype and 15 with a SZ phenotype, which indicates a deficiency in alpha 1-antitrypsin. Our data suggest a prevalence of 1.4% and 3.6% of Z and S alleles, respectively, in the French-speaking community of Belgium.