The Apt test for the detection of fetal haemoglobin in stool samples from neonates is described. This test has been previously reported to be helpful in the diagnosis of the swallowed blood syndrome in neonates, giving rise to 'melena neonatorum'. In this syndrome it is important to distinguish between swallowed maternal blood at the time of delivery from blood derived from the neonatal gastrointestinal tract. A spectrophotometric improvement has been made to the originally described Apt test, with additional recommendations for use.