The upper particle size limit of mineral floatability, is a parameter of great importance in the flotation process and the sharp decrease of flotation response when particle size approaches such a limit is a very well known phenomenon. The aim of this research was to find the most suitable hydrodynamic conditions to float coarse particles in microflotation tests. To reach such a target, the influence of some hydrodynamic parameters (Reynolds Number-Re, Froude Number-Fr, Weber Number-We and Power Number-Po) on microflotation response of coarse glass spheres (0.417-0.589mm, 0.208-0.295mm) and quartz particles (0.208-0.295mm) was studied in the presence of the collector ether amine acetate (75 mg/dm(3)) at pH=10. Maximum flotation response (almost 100%) was observed at 3,000 < Re <8,000; 0.1 < Fr <1.0; 10 < We < 100 and Po >0.54. For either more quiescent (Re <3,000; Fr <0.1 and We < 10) or more turbulent (Re >8,000; Fr >1.0; We > 100 and Po <0.52) hydrodynamic conditions, flotation recovery decreased steadily. Under more quiescent hydrodynamic conditions, the lower recovery was due to the fact that the impeller was not capable of keeping particles in suspension properly whereas under more turbulent conditions the disruption of particle/bubble aggregates was intensively observed.