Eighty-five regularly cycling women with normal ovaries at laparoscopy, were studied to determine the factors that influence the free androgen index (FAI). It was found that body mass index (BMI), age of the patient and the phase of the menstrual cycle that the blood was collected can all affect the FAI. It is recommended that where possible, specimens should be collected in the early follicular phase to avoid misinterpretation of the result.