320 adults and children of an isolated community of Bali, Indonesia, have been tested for blood groups ABO, Rh, MNS, P, Lewis, Duffy, Kell, for haptoglobin and transferrin and for hepatitis B surface antigen and antibodies. Phenotype distribution and gene frequencies are given for the total population tested and for two subgroups representative of the inbred population of the isolate and of the non-inbred part of the population. Significant differences between the two subgroups show a clear genetic drift in the inbred population. The study brings biological support to the ethnological hypothesis of population migrations in this area. Tests for hepatitis B surface antigen reveal a lower prevalence of the disease than in most other south-east Asian populations.