Isolation of a lipase produced by Pseudomonas aeruginosa (MW 29,ooo) employed cross flow microfiltration for production of a cell-free enzyme solution and cross flow ultrafiltration for concentration of the enzyme and removal of low molecular weight impurities. Poor flux and enzyme permeation were measured during initial screening of various microfiltration membrane types for isolation of the enzyme from a peptonized-milk-based broth; the results suggested that a soluble broth component was forming a gel layer which controlled both hydraulic flux and enzyme permeation. Reformulation of the fermentation medium resulted in enhanced performance, obtaining fluxes of 40 1/h m 2 and enzyme permeation of 50% on hydrophilically-modified PVDF membranes and resulted in a feasible clarification process. Enzyme permeation remained constant with respect to activity in the feed, rather than being proportional to activity in the retentate; it was hypothesized that this resulted from a concomitant concentration of the gel-forming components with cell concentration. Concentration of the clarified enzyme solution was performed using 3o ooo MWCO regenerated cellulose membranes. Complete enzyme retention and high flux (571/h m 2) were maintained through a 13o-fold concentration of the microflltrate. As both systems were taken to the loo and looo 1 scales, similar filtration performances were obtained with system hold-up volume and pump cavitation becoming important considerations at the larger scales. Excellent reproducibility was observed in a series of eight large-scale experiments.