To study the serum level of placental alkaline phosphatase activities in women with gynecologic malignancies, isoelectric focusing (IEF) technique was employed to differentiate isozymes of alkaline phosphatase (ALP). The proportion and absolute quantity of band 10 in isogram of ALP, which consists of placental alkaline phosphatase, was determined in 42 cervical cancer patients and 5 endometrial cancer patients preoperatively. Comparing with 33 controls, we found that serum placental alkaline phosphatase level was significantly higher in these patients. Moreover, using the 95th percentile value of placental alkaline phosphatase in the control group (17.76 U/L) as a cut-off point, the serum placental alkaline phosphatase positive rate in patients with cervical cancer is 47.6% and it is 80% in patients with endometrial cancer. Therefore, detection of serum level of placental alkaline phosphatase may be helpful for the diagnosis of these gynecologic malignancies.