Red cell haemoglobin (Hb), haematocrit (Ht), 2,3-diphosphoglycerate (DPG), and adenosine triphosphate (ATP) levels were measured in 876 individuals from six villages at two altitude levels (altiplano and coast) of the Departmento de Arica of Northern Chile. Of these, data on 761 individuals are subjected to analysis to search for the evidence of genetic adaptation to a hypoxic environment at a high altitude. Total phenotypic variance for each of the variables is higher at the altiplano as compared to their counterparts at the coastal level. Data on 1127 pairs of relatives of six degrees of relationships are used to determine the genetic component of variation in each of these four traits. To a certain extent the larger familial correlations as well as higher variances at altiplano are explained by the apparent assortative mating (which may again be due to their restricted population size) at the higher elevation. Yet, at least in three variables (Hb, Ht, and DPG) no reduction in the additive genetic component of variation is noticed at the higher altitude. ATP seems to have the highest degree of genetic component of variance, particularly at the coastal level. Some implications of these results are discussed in the light of their roles in the glycolytic pathway.