Confocal scanning laser microscopy (CSLM) was used to visualize two microfiltration membranes: a mixed eater (cellulose nitrate/cellulose acetate) 1.2 mum-rated membrane (150 mum thickness) and a reinforced nylon 0.45 mum-rated membrane (200 mum thickness). The microporous membranes were observed in their hydrated state, dry state or mounted in glycerol or in immersion oil. The agreement between the dry membrane and the hydrated membrane appears to be quite good. Careful selection of a mounting medium (glycerol, immersion oil) improves CSLM imaging. Optical sectioning of the nylon membrane mounted in immersion oil was performed at 1 mum intervals, from 0 to 60 mum. It was found that the pores located on the membrane surface were much larger than in the whole membrane. Optical sectioning of the ester membrane mounted in immersion oil was performed at 1 mum intervals, from 0 to 150 mum and a three-dimensional image was reconstructed from the optical serial sections. CSLM was found useful to delineate the exact morphology of these microporous membranes.