Although nausea and vomiting in early pregnancy is extremely common, very little information on the cause and course of this disorder is available in the literature. A prospective laboratory and clinical study of 102 consecutive healthy pregnant women was undertaken to evaluate nausea and vomiting in relation to clinical data, serum electrolytes, creatinine, total protein and hemoglobin. Multigravidae suffered from emesis gravidarum at a higher rate than did primigravidae. The frequency of emesis was especially high in women with short intergestational intervals. During pregnancy there was a decline in systolic blood pressure only in non-emetic women. The diastolic blood pressure in late pregnancy was significantly higher in emetic women than in non-emetic subjects. All laboratory values were within normal ranges. However, major changes occurred during pregnancy but some alterations were noted only in the emetic pregnancy. A different response to the hormonal situation is suggested to explain the dissimilarities between the emetic and non-emetic pregnancy.