To clarify the clinical significance of ultrasonography (USG) in the therapeutic course of invasive mole and choriocarcinoma, a detailed study of USG images from 31 patients, taken upon admission, in which an abnormal condition was clearly indicated, was undertaken. In addition, the clinical value of the pulse doppler and color doppler images used to determine the blood flow was also studied. The results revealed the following points. 1) Before the 1st therapy, USG conditions could be classified into three categories, type I (massive echogenic), type II (one or more echo free space (EFS) surrounded with a massive echogenic area) and type III (EFS). 2) A large number of patients with invasive mole exhibited type II, with a few exhibiting type III. A large number of patients with choriocarcinoma exhibited type I, and a few exhibited type II. 3) A comparison with PAG conditions showed a high correlation between the pooling image in PAG and the EFS in USG. 4) There was a positive correlation between the estimated volume of the tumor at the start of therapy and the hCG value in urine. In the chemotherapy patients, the reduction of hCG was accompanied by shrinkage of the tumor, and in 9 out of 22 patients (40.9%), the tumor disappeared on the USG at the point where the hCG became negative. 5) 14 of 22 chemotherapy patients (63.6%) matched the "Standard Progress" course, which was decided and based on the changes observed in the USG image over the course of chemotherapy.(ABSTRACT TRUNCATED AT 250 WORDS)