The effects of cyclic changes in feed water temperature and pressure on permeate flux, solute rejection, and compaction in spiral wound composite polyamide seawater reverse osmosis membranes were examined with pure water and 4% NaCl solutions. A membrane permeability hysteresis or memory effect due to the up and down temperature and pressure sequences was only seen with the saline water studies. However, the observed changes appeared to be reversible and were consistent with the Spiegler-Kedem/ Film Theory and the Kimura-Sourirajan Analysis/ Film Theory models. The overall results suggest that the net effect on permeance and solute rejection is the consequence of several interactions with feed/operating temperatures affecting membrane porosity and water/solute cluster size, and transmembrane pressure influencing membrane compaction.