ABSTRACT. Crab-eating monkeys (Macaca fascicularis) inhabiting Angaur Island, in the Republic of Palau, Micronesia, are said to be descendents of animals brought to the island about 80 years ago (Poirier and Smith, 1974). Field sampling was performed in November and December 1986 for somatometry, clinical inspection of hematological and parasitological characteristics, and genetic assessment of the monkeys' origin, in order to define their biological characteristics.In total, samples from 70 individuals were obtained in the field. Physically the island monkeys were smaller than animals that originated in Indonesia. A color variant, with hairs lacking brown shading, was observed in three of the captured animals. Hematological examination revealed that the mean number of leukocytes (WBC) was high and the mean erythrocyte count (RBC) and hematocrit value (Ht) were low. The appearance of helminth was so rare that only Streptopharagus sp. was found. Six different alleles were detected at the transferrin locus. The mean heterozygosity of the population was estimated to be 10.2%, suggesting a relatively high degree of genetic variability.