Bovine Spleen exonuclease (Phosphodiesterase II) excises 3'-phosphomononucleotides from oligonucleotides having a free OH terminus. The optimum pH for the enzyme is 5.5 using succinate and phosphate buffer and pH 6-7 with 0.1 M acetate buffer. Prepared from the 1mM sodium pyrophosphate, pH 6.9, alumina gel eluate of Hilmoe