In order to evaluate the clinical usefulness of maternal serum C-reactive protein measurement in early detection of infectious morbidity at term laboring women, serum C-reactive protein levels were measured in 521 healthy pregnant women : 64 who were not in labor before term, 55 who were in labor before term, 71 who were not in labor at term and 331 who were in labor at term. The frequencies of elevated serum C-reactive protein level were compared in relation to the gestational weeks, the presence or absence of labor, the status of amniotic membranes and the degree of cervical dilation. The obtained results were as follows. 1. The frequencies of women with elevated serum C-reactive protein, 0.8 mg/dl or higher and 2.9 mg/dl or higher, in 521 health pregnant women were, 12 % and 4 %, respectively. 2. C-reactive pretein levels of 0.8 mg/dl or higher were more frequent in the group of women in labor than those not in labor(5. 93 %, vs, 13.73 %, p<0.05), but the frequencies of C-reactive protein level of 2.0 mg/dl or higher were not statistically different between both groups. The frequencies of C-reactive protein level of 0.8 mg/dl or higher and 2.0 mg/dl or higher were not statistically different between the groups before term and at term, intact and ruptured membranes, latent phase and active phase of labor, respectively. 3. Before term, C-reactive protein levels of 0.8 mg/dl or higher and 2.0 mg/dl or higher were more frequent in the group of women in labor than those not in labor(23.64 vs. 4.69, p<0.001 and 12.73% vs. 3.13%, p<0.05, respectively), but those statistical differences were not seen between both group at term. Above results and review of literature suggest that serum C-reactive protein level of 2.0 mg/dl or higher may be reliable in early detection of infectious morbidity at term laboring women as well as laboring women before term, and the presence of subclinical infection should be suspected in the laboring women before term with serum C-reactive protein level of 0.8 mg/dl or higher.