The theory that the Th1 and Th2 cell ratio shifts towards Th2 dominance during pregnancy may improve fetal survival has gained support from recent studies. Also, the variation in the Th1/Th2 cell ratio is reportedly associated with intrauterine growth retardation and preeclampsia. On the basis of these findings, the analysis of the Th1/Th2 balance may be useful in predicting severe complications during pregnancy. However, simple methods for the analysis of Th1/Th2 balance are presently not available. Recently, it has been reported that regulation of CD26 cell surface expression correlates with the production of Th1-like cytokines. On the other hand, previous studies proposed that the sCD30 molecule is an activation marker useful for evaluation of a Th2 immune response. It is, therefore, possible that the analysis of the Th1/Th2 balance during pregnancy by measuring plasma sCD26 and sCD30 simultaneously is a simple and useful method. We herein demonstrate that combined analysis of sCD26 and sCD30 is a potent surrogate tool to evaluate the Th1/Th2 balance during pregnancy.