The electrophoretic mobility in paper of 3 antituberculous chemotherapeutic agents and their principal metabolites are described. The mobilities of these compounds under the conditions found optimal in this study are reported. Photographs showing the separation obtainable in paper with the systems described are presented, and the retarding effect of the serum proteins on the electrophoretic mobility of the compounds is discussed. Variability of recovery of the compounds by elution from the filter paper after electrophoretic separation was the greatest handicap encountered.