Blood was taken from 100 consecutive asymptomatic women at 17 to 18 weeks of pregnancy for Kleihauer testing. When a proportion of these slides were assessed at a different hospital there was agreement in only 46%. When the number of fetal cells were quantified there were differences of over 500%. These results show a large niter-observer and inter-hospital variation in interpreting Kleihauer slides. If these investigations are to be performed, it is essential that clinicians can rely on the results. There is a need for quality control measures and audit so that laboratories can rectify any deficiencies in their techniques.