The effects of operating variables on permeation flux and resistances for the ultrafiltration of passion fruit juice were studied. The experiments were carried out on a polysulfone hollow fibre membrane laboratory module. The results showed that flux increased with temperature from 30 to 40 degrees C and then decreased at 50 degrees C. At low temperatures (30 and 40 degrees C) the flux-pressure curves followed the gel-polarization model. The results were different at 50 degrees C where flux initially increased with pressure and then subsequently decreased. It was also observed that flux increased with increasing bulk flow rates and decreased with increasing bulk concentration, in accordance with concentration polarization models. Except for membrane resistance R(m), which was constant, other resistances increased with pressure and juice concentration and decreased with flow rate. An increase of temperature reduced the values of R(p,re), the reversible polarized layer resistance and R(p,it), the semi-reversible polarized layer resistance but enhanced R(f), the fouling resistance. R(p,re) was the major resistance which controlled the permeation flux for low temperature operation. At high temperature (50 degrees C) the reversible polarized layer changed to a cross-linked gel and R(f) was significantly increased.