The computerized scanning electron microscope system (QEM*SEM) as developed for characterizing whole mineral particles by the CSIRO Division of Mineral Chemistry, Institute of Energy and Earth Resources, has proved to be a very useful tool in the analysis of products and intermediate samples in the Lead-Zinc Concentrator of Mount Isa Mines Limited. Two examples of the application of the method are given in the present paper. The analysis of final cleaner concentrates from two distinct ore blends has indicated that in each case most of the galena in the 10–37μm size range is fully or nearly fully liberated. This proportion decreased down the third cleaner cell bank. Coarser particles, in the 37–53μm size range, were shown to have smaller proportions of galena in the highly liberated galena classes. The remainder of the galena in each case is spread over the lower galena classes, which become increasingly interlocked with gangue. Significant proportions of gangue, both sulphide and non-sulphide were also found to be free or almost free from interlocking with galena, especially in the 10–37μm size fraction. Thus lack of selectivity, as well as composite particle flotation, is seen to be responsible for downgrading of lead third cleaner concentrates. In addition, the QEM*SEM technique has shown that the distribution of galena intergrowth in lead first cleaner tailings is spread over most composite classes, more akin to regrind/retreat particles than to lead primary rougher tail particles. Thus QEM*SEM provides a valuable method in the mineral industry of today of measuring the relative degree of liberation of ground ore or flotation products, and the extent of dilution of concentrates by non-selective flotation of liberated gangue. Full liberation is not always desirable because of the cost of grinding to the finest sizes and because non-selective dilution of concentrates by fine liberated gangue often increases. QEM*SEM can also play a useful role in deciding the best destination for intermediate concentrator streams.