We examined the serum CA130 level in women in early pregnancy with normal (n = 13), and abnormal (n = 28) course. The abnormal course consisted of intrauterine spontaneous abortion (n = 10), hydatidiform mole (n = 3) and tubal pregnancy (n = 15). The serum CA130 level was higher than for normal nonpregnant women (35u/ml) in 69% (9/13) of women with normal pregnancy, 90% (9/10) of those with intrauterine spontaneous abortion and 100% (3/3) of those with hydatidiform mole; the mean value and standard deviation for these three groups were 131 +/- 150u/ml (n = 13), 197 +/- 253u/ml (n = 10), and 47 +/- 15u/ml (n = 3), respectively. In contrast, the serum CA130 level of the 15 women with tubal pregnancy was 28 +/- 21u/ml. Among these patients, all of the 13 women without genital bleeding had a CA130 level within the normal range for nonpregnant women (mean +/- SD; 20 +/- 6u/ml). Since CA130 is abundant in the decidual tissue but is scant in tubal tissue, a high CA130 level in maternal sera during early pregnancy may indicate the presence of the destruction of decidual tissue, while a low or normal CA130 level throughout early pregnancy is regarded as characteristic of tubal pregnancy.