Abstract Thin-layer chromatographic separations on a new layer, microcrystalline cellulose “Avicel”, and on DEAE-cellulose are presented. They include: 1. 1. R F values of 15 bases and methylated analogues of the bases in six different solvents, of 11 nucleosides in 5 different solvents, and of 8 nucleotides in two solvents. 2. 2. Separation of mixtures of deoxynucleoside and ribonucleoside, mono-, di-, and tri-phosphates of the adenine, guanine, uracil, and cytosine series. 3. 3. Separation of mixtures of the four ribonucleoside 2′,3′-monophosphates, of the four ribonucleosides 5′-monophosphates, and of the four deoxyribonucleoside 5′-monophosphates. The advantages of microcrystalline cellulose over other materials for thin-layer chromatography are discussed.