The distribution of C3 phenotypes in the population of Veneto was investigated by electrophoresis on agarose gel. In our sample (n = 810) the three common phenotypes C3 SS, C3 FF and C3 FS and a further phenotype, C3 S-VF, were observed. The following gene frequencies could be calculated: C3S = 0.8068, C3F = 0.1926 and C3V = 0.0006. These frequencies have been compared with those found in other populations. The analysis of 21 mother-child pairs was in agreement with an autosomal codominant inheritance.