Sickle-cell disease is usually complicated by vaso-occlusive attacks. A review of the case-histories of 26 patients permitted an analysis of 92 severe attacks. We compared the outcome of 52 attacks treated with hyperhydration associated with a modifying erythrocyte membrane agent (pentoxifylline), with 40 attacks treated with hyperhydration and other drugs. This result compares well the current knowledge of the rheologic mechanisms involved in vaso-occlusive attacks of sickle-cell disease.