Dear Sirs, the comments made by Professor Reali1 on the Case Report, “Anti-D immunisation with permanent biological damage following inadequate post-amniocentesis prophylaxis2” are all pertinent and I thank him for the attention he gave to the report and for the occasion to make some precisions on the case presented, which was an example of failed prophylaxis with anti-D IgG, since it is now known that amniocentesis can act as a stimulus to maternal immunisation because of the possibility of repeated transplacental haemorrhages. Before submitting the case we considered other possible causes of the failure of the prophylaxis and, on the basis of the official documentation and the information provided directly by the patient, we were able to be sure that the prophylaxis was truly administered and at the right time. The initial serological examination was carried out twice with the same outcome (negative), the method used in the hospital which referred the patient is the same as that used in our centre (microcolumn agglutination test) and we have no reasons to doubt the correct performance of the test. It seems impossible that the dose of anti-D IgG was different from that declared and recorded, since there are no other doses of anti-D IgG in the referring hospital. For all the above reasons and because of the outcome, we felt that it was useful to report this as a case of failed prophylaxis attributable to a discrepancy between the antigen load in the mother and the amount of antibodies injected. It is, in fact, agreed that the dose of the treatment should be commensurate with the entity of the foetal-maternal haemorrhage3, and it is known that inadequate prophylaxis is the most frequent cause of failure of treatment. We, therefore, felt that it was worth drawing attention to the need to carry out a quantitative evaluation of foetal-maternal haemorrhage also in cases of amniocentesis and/or trauma during pregnancy, just as we feel that it is safer to adapt the therapy to the amount of haemorrhage, rather than injecting a single, arbitrarily chosen dose, because of the numerous variables that can have effects and because of the severity of the consequences of immunisation, which can lead, as in our case, to permanent biological damage.