ABSTRACT. Three polar desert lakes (Lake Fryxell, Lake Hoare, and Lake Vanda) in the dry valleys of Antarctica were studied to determine relations between source and composition of dissolved organic matter in lakes with different physical, chemical, and biological characteristics. Profiles of dissolved organic matter in the water column, calculations of streamflow contribution of dissolved organic matter over the age of the lakes, inorganic profiles, and dissolved organic material fractionation results are discussed in relation to autochthonous versus allocthonous source. Chemical characteristics of the major dissolved organic carbon fractions (fulvic and hydrophilic acids) are very similar among lakes and may reflect the overwhelming influence of precursor compounds on the chemistry of microbially derived hydrophilic and fulvic acids. The differences between lakes are explained in terms of the dominant processes in the three dry valley lakes.