Smoking during pregnancy is a significant public health issue, and studies of the effectiveness of interventions to reduce maternal smoking require accurate measurement of smoking status. This study addresses some key issues in improvement of the effectiveness and efficiency of chemical validation of smoking status using a simplified high-pressure liquid chromatography urine cotinine method. Urine samples were collected from pregnant women enrolled in a smoking cessation trial and from non-pregnant volunteers exposed to environmental tobacco smoke (ETS). Analysis of ETS samples produced a maximum cotinine of 28 microg/mmol creatinine, which was established as the cut-off point for this method. This method is a relatively fast and inexpensive technique with which to analyse large batches of cotinine samples and can reliably measure smoking status.