Background: Premature rupture of membranes is a common complication of pregnancy with an approximately 5 to 8% incidence rate. The diagnosis is based on clinical history with apparent amniotic fluid in vagina. In suspicious cases, especially when nitrazine and ferning tests are not helpful, applying highly accurate, inexpensive, and rapid tests including vaginal fluid creatinine and ß HCG will be of great importance. This study aimed to measure the ß HCG level of washing solution in women with PROM and also in women with normal pregnancy, and to determine the mean in each group in order to diagnose PROM.
 Material and Methods: In the present study, 60 pregnant women were divided into two groups of those with PROM and those with normal pregnancy who were all homogeneous in terms of gravidity, parity, mother's age, and gestational age. After the posterior fornix was washed with 3 milliliters of normal saline, the fluid in the same syringe was aspirated again and its ß HCG level was measured. The data were analyzed using the SPSS software and U-Mann-Whitney test, and t-test.
 Findings: The mean for ß HCG level in PROM was 496.4 mIu/ml, and in normal pregnancy it was revealed to be 8.85 mIu/ml. The difference between the two groups regarding ß HCG level was significant.
 Conclusion: Consequently, in suspicious cases of PROM especially when nitrazine and ferning tests are not helpful, levels of ß HCG in vaginal fluid can be useful to diagnose PROM