A qualitative and quantitative comparison of perchloric acid (PCA) and trichloroacetic acid (TCA) extraction procedures of biologic material containing cytosine arabinoside (Ara-C) and 1-beta-D-arabinofuranosyluracil (Ara-U) and their biologic 5'-phosphate derivatives revealed definite superiority of the PCA procedure over the TCA procedure. High-pressure liquid chromatography provides rapid and accurate quantitative and qualitative separation of both Ara-C and Ara-U and their 5'-mono-, di-, and tri-phosphates (mu Bondapak NH2 column), or their 5'-mono-, di-, and tri-phosphates without nucleosides (ABX Permaphase columns).