This study presents results of bench flotation tests on pentlandite-pyrrhotite separation using a Ni-Cu sulphide ore sample, where the crystal structure of pyrrhotite is predominantly hexagonal (e.g., 90-95%). The hexagonal structure of pyrrhotite is known to be more floatable compared to the monoclinic form and is thus recognized as a more challenging separation issue. In order to provide a more complete understanding and capability of the sodium metabisulphite (SMBS)-triethylenetetramine (TETA) reagent systems, particle size effects were investigated. The recovery by size response was compared for SMBS, TETA and their combinations with amyl xanthate as a collector. The pyrrhotite recovery for all sizes are lower than that of pentlandite for the blank case as well as individual cases with SMBS and TETA. For pyrrhotite, the recovery by size relations in the case of individual uses of these reagents were mainly determined by recovery losses at coarser size range (> 74 mu m), which occurs at a coarser size for pentlandite (> 212 mu m). The combined use of SMBS and TETA very significantly knocked down the pyrrhotite recovery to less than 7% that was a maximum for the - 10 mu m size range (attributable to hydraulic entrainment). High recovery of pentlandite in a wide range of intermediate sizes and drastically low recovery of pyrrhotite resulted in a very efficient separation of pentlandite from pyrrhotite in all sizes.