Supported polymeric liquid membranes with polypropylene glycol as the liquid phase were tested for extraction of p-nitrophenol from an aqueous wastestream. Transient experiments with small flat sheet membranes were used to determine the membrane permeability and the diffusion coefficient in the liquid phase. The process was then scaled up using hollow-fiber radial-flow modules, first in the laboratory and then under plant conditions. When boundary layer resistance and membrane accumulation and depletion were allowed for, the results obtained were consistent with predictions based on the data for flat sheets.