The relationship between oral temperature taken at the time of admission and the duration of elapsed labor was evaluated. Onset of labor data revealed a diurnal distribution with an apogee at midnight to 2 AM and a nadir at 11 AM to noon. Temperature data ranged from 94.3 degrees to 99.7 degrees F (34.6 degrees to 37.6 degrees C). The mean temperature of 97.8 degrees +/- 0.8 degrees F (36.6 degrees +/- 0.44 degrees C) is significantly lower (p less than 0.001) than the clinical reference temperature of 98.6 degrees F (37.0 degrees C). A likely explanation is the coincidental admission time (early to late morning) and the nadir of the diurnal variation in temperature. Linear regression fitted to the data (after deletion of six hypothermic outliers) yielded the relationship: temperature = 97.8 degrees F + 0.0115 X duration of elapsed labor (temperature = 36.6 degrees C + 0.0064 X duration of elapsed labor) for which the correlation coefficient is not statistically significant.