A simple diagnostic procedure in haemoperitoneum, using a single drop of fluid collected by abdominal tap and placed on a glass slide, is described. It is possible in this way to demonstrate the presence of minimal bloody effusions and to radically decrease the number of false negative results of paracentesis. Taps considered to be blood-free thus fall within the category of positive results. The actual procedure is improved since it is no longer necessary to collect a relatively large volume in order to ensure the diagnosis of haemoperitoneum. Furthermore, more complicated methods using catheters, with or without lavage, may be avoided.