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Controlled deficit irrigation (CDI) has been studied in a sugar beet crop cultivated in a semi-arid zone. Eight drip irrigation treatments were differentiated by the level of fulfillment of the water requirements. The effect of deficit irrigation at three crop stages (vegetative development, root swelling and ripening) has been studied. Total productions and their industrial quality index (IQI) have proved to be not influenced by the total volume of irrigation water. On the other hand, as expected, highly significant differences do appear in connection with the water use efficiency (WUE) of the total volume received which has ranged from just over 130-170 kg ha(-1) mm(-1). The treatments to be regarded as advisable are those which, like T-8, cause medium, moderate and severe water restrictions in the development, root swelling and ripening periods, respectively. This treatment has enabled us to achieve high yields (up to 117.64 t ha(-1)) with fairly moderate water consumption rates (6898 m(3) ha(-1)). Other strategies, such as those used in T-6 or T-7, which maintain, like the above, parallel criteria, though more moderate when it comes to bringing about water restrictions, can be used because of the high yields obtained and their remarkable WUE, particularly in the case of T-7. On the contrary, strategies with no water restrictions in the early stages, are to be regarded as less advisable, because of its low efficiency or due to its high water consumption which has not led to significantly higher output or better quality. (C) 2003 Elsevier Science B.V. All rights reserved.