SYNOPSIS.Culture forms of 9 species of Trypanosomatidae were studied. Of these,Crithidia fasciculata, Leishmania brasiliensis, L. donovani, L. tropica, Trypanosoma conorhini, T. cruziandT. rangeliconsumed significantly less glycerol than glucose, both when the 2 substrates were offered singly or simultaneously. On the other hand,T. gambienseandT. rhodesienseconsumed as much glycerol as glucose when the 2 substrates were given separately. When both substrates were offered simultaneously, more glycerol than glucose was consumed, but the sum of glucose + glycerol carbon taken up approximated closely that taken from glucose alone. This held for species consuming only little glycerol, indicating that in all cases some mutual inhibition took place. Atttempts to adaptT. cruzito glycerol consumption were unsuccessful. WhenT. gambienseandT. rhosiensewere cultivated in the presence of glycerol, their normrapid glycerol consumption remained also unchanged but, curiothey consumed more glucose than before “adaptation.” Iodoacetami and NaF strongly inhibited glucose and glycerol absorption of 7gambiense; phloridzin, deoxygalactose and deoxyglucose gave nonificant inhibition. KCN slightly stimulated glucose absorption, weakly inhibited glycerol absorption. Omission of sodium from medium was without effect, while lack of CO2markedly inhiglucose and glycerol uptake. Galactose was not a satisfactory sub strate forT. gambienseandT. rhodesiense, nor were deoxygalactos and deoxyglucose. These 3 hexoses were consumed in small amonly and did not allow maintenance of motil