The use of warm water immersion (WI) by women for relaxation during labor is being used around the world; however, there is little available research as to the effects of WI. We conducted this prospective, randomized, and controlled study to determine the safety and effect of WI on the woman in labor. We studied 93 subjects between 36 and 41 weeks' gestation, in active labor, with intact membranes, and without major medical or obstetric complications. Subjects in the WI group utilized a tub in labor along with other pain relief measures such as ambulation, rest, showers, and analgesics. Subjects in the no-WI group could use all available methods of pain relief except WI. Water immersion did not alter the rate of cervical dilation, change the contraction pattern, change the length of labor, or alter the use of analgesia. The rates of chorioamnionitis and endometritis were not altered by WI. Although we did not demonstrate an improvement in progression of labor by WI, there was no evidence of increased maternal, neonatal, or infectious morbidity.