Pyrrhotite (Po) is a common gangue mineral in Ni-Cu sulphide ores (pentlandite {Pn}-chalcopyrite {Cp}) and can be difficult to reject under certain circumstances. This paper summarizes the results of a lab-scale flotation study on a reactive ore with a high Po/Pn ratio (7.5), 42 % hexagonal Po content (of total Po), and 85.9 % Ni deportment in Pn (remainder Ni largely reporting to Po), making Po rejection challenging and Ni recovery/grade targets difficult to obtain. The main objective was to assess whether the ore could be processed "as received" to achieve high Pn recovery (>85 %) while ensuring low Po recovery (<20 %), which will typically yield acceptable final concentrate grades after cleaning stages. Baseline testing showed Po depression was difficult by conventional means and required depressants. The test work was centered around the use of DETA (diethylenetriamine) for its proven effectiveness for Po depression (used with sodium metabisulphite (SMBS)). Several strategies were tested: DETA alone; DETA/SMBS; sulphuric acid/DETA/SMBS with/without aeration; and DETA/SMBS with concentrate regrind. The DETA was found to be effective as a Po depressant (both hexagonal and monoclinic Po) on this challenging ore. Overall, the DETA/SMBS with concentrate regrind exhibited the best results (similar to 11 % Po recovery at similar to 85 % Pn recovery) and was found to be sufficient in achieving the outlined targets.