This study investigated the aetiology of nausea and vomiting in pregnancy (NVP) in primary care using a new methodology. Eighteen women in early pregnancy had 2 blood samples taken in one 24-hour time period, one when they were symptomatic, and another when they were symptom-free. Maternal serum levels of the candidate agents PGE2, IL-1β, and TNFα were measured. The study shows a positive relationship between NVP and maternal serum PGE2 levels in early pregnancy.