The absorption of 3H-labeled adenine, adenosine, hypoxanthine, and 14C-labeled inosine by normal rat erythrocytes, P. berghei-infected erythrocytes and saponin released free parasites was measured. The uptake of these labeled substrates by normal rat erythrocytes occurs both by diffusion and mediated transport systems. Similar absorptive mechanisms for these substrates were observed for both P. berghei-infected erythrocytes and free parasites. Data from inhibition studies using purine base and nucleoside analogs indicate the presence of 3 distinct transport loci in the normal erythrocyte for adenosine-inosine, hypoxanthine, and adenine and 2 loci in the infected erythrocyte and free parasite for adenosine-inosine-hypoxanthine and adenine. The initial metabolism of 3H-adenosine by the free parasite was also examined. A double isotope technique was used to follow the separate metabolic fates of the purine base and ribose moieties of adenosine. The data suggest a possible conversion of adenosine to the purine base and ribose moiety and subsequent uptake of the purine base by the parasite. A powerful adenosine deaminase inhibitor (2-deoxycoformycin) significantly reduced the uptake of 3H-adenosine by the free parasites. Chromatographs of aliquots from postincubation media show the tritium label to be associated predominantly with adenosine in the presence of 2-deoxycoformycin and with inosine and hypoxanthine in the absence of the inhibitor.