Gintzler found an abrupt increase in pain thresholds in rats during the last days of gestation. While some data suggest a similar increase in pain thresholds for pregnant women, Goolkasian and Rimer have found, using signal detection procedures, that women are increasingly likely to report stimuli as painful during the last 2 weeks of pregnancy. The present studies were carried out to assess pain and discomfort thresholds in the last weeks of women's pregnancies. In the first study, daily measures of the pressure-induced pain thresholds of 6 women who had spontaneous, vaginal births increased during the last 16 days of pregnancy and exceeded the 300 mm Hg maximum stimulus pressure for the last 9 days of pregnancy. In the second study, the discomfort thresholds of 6 women were measured each day during the last 11 days of pregnancy before spontaneous vaginal births. The discomfort thresholds of the pregnant women were higher than those of 6 non-pregnant women whose discomfort thresholds were also measured each day. Pregnant women's thresholds increased before the onset of labor, while the discomfort thresholds of the non-pregnant women were unchanged during the course of the study. These results extend Gintzler's findings of reduced sensitivity to pain shortly before parturition.