We describe a method for calculating blood loss at vaginal delivery using a special plastic drape. Blood loss is calculated from the sum of three components: (1) blood lost in sponges, (2) blood loss represented by clots, and (3) blood loss represented by unclotted RBC. The procedure has been used in ten patients and the results are presented. The obstetrician would know the maximal potential blood loss immediately after delivery. If this figure is less than 15% of the estimated blood volume, further calculation might be deemed unnecessary. If this figure exceeds 15% of the estimated blood volume, however, the full procedure described should be done. The final result could be available to the obstetrician within approximately four hours after delivery.