An experimental investigation was carried out to study the periodic operation of a reverse osmosis water desalination unit with a spiral-wound membrane. The operating pressure was varied according to a symmetric square wave function around time-average values of 40 and 50 bars. Time periods ranging from 5 to 15 minutes and amplitudes of 5 and 10 bars were investigated. The results of these periodic tests were compared with results obtained from the conventional steady-state mode of operation. It has been found that the cyclic operation leads to higher time average permeate flow rates than that obtained from the corresponding steady-state operating conditions. It has also been found that the permeate rate increases with increasing amplitudes and decreasing time periods of the forcing function. For the considered amplitudes and periods, the improvements in the sweet water production rate ranged from 0.3 to 13%. These enhancements in the permeation flux have been obtained at I the expense of marginal increases in the power requirements. As for the product quality, the concentration of salt in the permeate did not exhibit any specific trend The value of salt rejection ranged from 98 to 99%.