Although nausea and vomiting associated with early pregnancy are extremely common, the causal factors remain obscure. An endocrine etiology for this problem persists as a popular but unproved theory. The present study exn (hCG) and 17-hydroxyprogesterone (17-OHP) and the presence or severity of nausea and/or vomiting in women in the first 16 weeks of pregnancy. The occurrence and severity of nausea and/or vomiting in women with hydatidiform moles in relation to serum hCG levels were also investigated. Levels of hCG and 17-OHP in pregnant women grouped on the basis of severity of nausea and vomiting are compared to each other and to the levels found in normal pregnancies. No relationship could be established between the levels of hCG and 17-OHP and the incidence and severity of nausea and vomiting in either pregnant patients or in women with molar pregnancies.