The results of screening sera from 136 healthy Norwegian blood donors by means of an agarose gel‐electrophoresis technique with respect to the phenotypes within the C'3 polymorphism are reported. The different phenotypes were easily recognized, and the distribution of phenotypes among unrelated individuals was in agreement with the expectancy from Hardy‐Weinberg equilibrium. A frequency of 0.14 for the postulated geneC31and of 0.84 forC32was found. In five of the 136 samples tested, rarer genes (two different) had apparently contributed to the phenot