The symptoms of nausea and vomiting in pregnancy were described by 363 pregnant women who kept daily symptom diaries. All delivered a single live baby. The majority of information collected was prospective, with the median day from last menstrual period to initial interview by the study midwife being day 57. It was found that 80% of women had symptoms, 28% experienced nausea only, while 52% had nausea and vomiting. The mean number of days from last menstrual period to onset and cessation of symptoms was 39 and 84, respectively, and 40% of women's symptoms ended abruptly. Cessation of symptoms occurred at approximately the same day from the last menstrual period whether they had begun early or later, severely or mildly [corrected]. The median total number of hours of nausea per pregnancy in those 292 women experiencing symptoms was 56, with peak symptoms occurring in the ninth week. Eighty five per cent of women experienced days with two episodes of nausea. Fifty three per cent of episodes of vomiting occurred between 06.00 hours and 12.00 hours. The symptom complex can be defined as episodic daytime pregnancy sickness. Among the study population, 206 women were in paid employment. Seventy three of these women (35%) spent a mean of 62 hours away from their paid work because of symptoms of nausea and vomiting, showing the socioeconomic significance of this condition. The detailed information gathered should help in the investigation of the aetiology of nausea and vomiting during pregnancy.