1. Relative to rabbit erythrocytes, chicken red blood cells exhibit a much greater capacity to utilize [3H]adenine for nucleotide synthesis in vitro, even at 5 degrees C and in the absence of added inorganic phosphate. 2. This difference is largely due to a higher concentration of phosphoribosylpyrophosphate and greater activity of adenine phosphoribosyltransferase in the avian cells. 3. The capacity of avian erythrocytes for utilization of guanine and hypoxanthine is several fold less than that of adenine. 4. The data are consistent with lower activity for hypoxanthine/guanine phosphoribosyltransferase than for adenine phosphoribosyltransferase in intact chicken erythrocytes. 5. The results indicate that reutilization of adenine by chicken erythrocytes may be physiologically significant.