A retrospective review of 64 patients receiving more than 10 units of red cell concentrate plus crystalloid within 12 h revealed two consecutive patterns of elevation of the partial thromboplastin time (PTT). The PTT at 3 to 4 h (PTT3-4) correlated with the number of liters of crystalloid (LC) infused over the first 3 h (PTT3-4 = 37 + 7 LC, r = .7643, p less than .001); the PTT thereafter (PTT4+) correlated with the number of hours of closely antecedent hypotension (AH) (PTT4+ = 37 + 21AH, r = .8680, p less than .001). These data indicate a transient dilutional coagulopathy, followed by coagulopathy related to the duration of closely AH. Whether this latter is due to impaired production, disseminated intravascular coagulation, or dilution due to internal shifts of fluids and/or proteins, remains to be clarified. Therapeutic implications of these data are discussed.