Nausea and/or vomiting in early pregnancy is common enough to be generally accepted as normal or 'physiological'. The specific etiology of these complaints is still obscure. One possibility is that endocrine factors may play some part. In this study, 102 healthy pregnant women, of whom 62 complained of nausea, were followed throughout pregnancy and the circulating levels of cortisol, testosterone, dehydroepiandrosterone sulphate (DHEA-S), progesterone, oestradiol and total and free oestriol were measured. In early pregnancy, serum levels of cortisol and progesterone were significantly lower in emetic subjects. In the last trimester, significantly higher DHEA-S concentrations and lower testosterone values were found in women who had suffered from nausea and vomiting in early pregnancy compared to asymptomatic subjects. Overt differences were found between emetic and non-emetic pregnancy and it is concluded that endocrine factors are of etiological importance in emesis gravidarum.