The isozyme type 2 of acid a-glucosidase, identified by "affinity" starch gel electrophoresis, was found to have a gene frequency of 0.001 in an unselected Greek population from Southwestern Greece. The estimated frequency of the heterozygote in the population is 1 in 500 and of type 2 homozygote 10(-6). This frequency is by far lower than that reported in Europeans and other populations. This may be a characteristic of the Greek gene pool at the acid a-glucosidase locus or it may be present in populations of neighbouring countries as well.