Since a report in October 2007 of dramatic improvements in trauma mortality in a military population when massive transfusion of red blood cells (RBC) was accompanied by plasma replacement at 1:1 proportions, interest in the plasma-to-RBC ratio during resuscitation in both the trauma and transfusion communities has been intense. Over the 7-month period from August 2008 through February 2009, a further 9 major studies examining experience with plasma replacement in massively transfused civilian trauma patients have been published. This flood of observational studies is likely to continue. In this review, the authors examine the findings of these initial studies, highlighting the epidemiologic and analytic methodologies used, and the likely influence of these methodologies on the reported outcomes.