In many small populations completely random fluctuations in the frequencies of certain alleles or gene combinations may occur, even under constant environmental conditions. These fluctuations constitute genetic drift or Sewall Wright effect. The potential role of drift in microevolution is considerable. Dunker religious community in Pennsylvania (U.S.A.) comprises a small population. The gene frequencies at several loci deviate strongly from those found in the surrounding population and in the population from which the group was originally derived (West Germany). Drift is tentatively considered to be responsible for these deviations.