The aim of the present study was to review published surveys on allelic frequencies S and Z in Spanish populations to evaluate the validity of the reported data. Thirty-four studies published since 1965 were retrieved by MEDLINE, Index Medicus and consultations with experts. The criteria for studies selection were (i) sample size > or = 250 individuals; (ii) alpha-1-antitrypsin phenotyping determination performed by means of crossed antigen-antibody electrophoresis or isoelectrofocusing; (iii) S and Z reported outcomes with an upper 95% CI smaller than mean + 2 SD, a lower 95% CI smaller than mean - 2 SD, and the following ratio: 100 x (95%CI upper limit - 95%CI lower limit)/allelic frequency, for both S and Z, included in the mean +/- 2 SD interval. Thirteen out of 34 surveys retrieved complied with the proposed criteria for S gene frequency analysis and 11 fulfilled the criteria for Z. The greatest frequency for S type is in the north-west of the country (149 alleles per 1000 in Galicians natives), while frequencies in the rest of the country are approximately 100 alleles per 1000. The greatest frequency for Z type has been reported in newborn infants from Valladolid (20.8) and in a randomly selected general population of Asturias (19.7). In the rest of Spain, Z frequencies range from 1.5 to 15 alleles per 1000 genes.