A serious shortage of nurses has developed since 1984 despite a growing number of employed nurses and a substantial decline in the number of hospital inpatient days. The evidence suggests that the shortage is the result of an increased demand for nurses, not a decline in supply. The increased demand in large part has resulted from the substitution of registered nurses for licensed practical nurses, aides, and other patient services personnel. The substitution was feasible because nurses' wages have been depressed compared with those of other hospital employees. The shortage is likely to abate if nurses' wages increase, making substitution more costly. Even in the absence of continuing wage increases, hospitals could ease the shortage by restructuring patient services and enabling nurses to spend a greater portion of their time in direct patient care.