Fundamental operating parameters and column performance have been measured on the interlinked, four-column cryogenic distillation system at the Tritium Systems Test Assembly. Using mixtures of hydrogen and deuterium, data have been gathered and are given here on liquid holdup in the column packing and liquid level in reboilers (factors important to isotope inventory), pressure drop in the column packing, and product purity. Both Raman spectroscopy and gas chromatography were used for product analysis.