The influence of maternal position during labor on comfort and uterine efficiency was studied by contrasting the influence of sitting in a chair with lying on the side during the first stage of labor. Nineteen primigravidas alternated between these two positions at 30 minute intervals for as long as this was possible during their labors. There was a significant difference in their preference to sit up during early labor (less than 6 cm dilation) and lie on their side during late labor (greater than 6 cm dilation). Uterine efficiency, however, was significantly less (p less than 0.05) in early labor in the sitting position than on the side. After labor was well established, ie after 6 cm dilation, the efficiency of uterine contractions to dilate the cervix was not significantly different between the 2 positions although it was less in the sitting position. The lateral recumbent position was accompanied by more efficient labor and was preferred by most women in late labor. Localization of pain and fetal position also seem to be associated with maternal position preference, and both factors require further investigation.