The purpose of most screening and diagnostic tests is to initiate treatment when a problem is found and, otherwise, to allay anxiety. The extent to which the second of these objectives is met was studied in a prospective study of 179 pregnant women. Women who had amniocentesis to detect Down's Syndrome or were screened for a fetal neural tube defect had significantly lower anxiety levels in the third trimester of pregnancy than women who did not undergo these tests. Undergoing screening for a neural tube defect was also associated with a more positive attitude towards the pregnancy in the second trimester. These results suggest that the previously reported raised levels of anxiety in women undergoing such tests do not necessarily remain high for the duration of the pregnancy and, indeed, undergoing testing may serve to protect women against high levels of anxiety in the third trimester of pregnancy.