Objectives: To determine the effects of resuscitation with the colloidal solution (hydroxyethyl starch) vs. crystalloid solution on cell-mediated immune functions after trauma-hemorrhage. Design: Prospective, multiexperimental, randomized, controlled study. Setting: University research laboratory. Subjects: Thirty-six inbred male C3H/HEN (endotoxin-sensitive) mice, aged 6 to 7 wks, and weighing 18 to 23 g. Interventions: Crystalloid (lactated Ringer's solution) with and without 6% hydroxyethyl starch after trauma-hemorrhage. Measurements and Main Results: Mice underwent laparotomy, were bled to and maintained at a blood pressure of 40 mm Hg for 60 mins, then resuscitated with either 4x the shed blood volume as lactated Ringer's solution or 2x the shed blood volume as lactated Ringer's solution plus 1x 6% hydroxyethyl starch. Sham mice were neither hemorrhaged nor resuscitated. At 2 or 24 hrs posthemorrhage, serum, splenocytes, peritoneal macrophages, and splenic macrophages were obtained. Bioassays were used to determine interleukin-2, interleukin-3, and interleukin-6 concentrations, while splenocyte proliferation was assessed by 3H-thymidine incorporation. Trauma- hemorrhage markedly depressed splenocyte proliferation, interleukin-6 release by macrophages, and lymphokine release at 2 and 24 hrs postresuscitation. The combination of lactated Ringer's solution and hydroxyethyl starch neither restored, nor exacerbated lymphocyte functions. Interleukin-6 release by peritoneal macrophages was restored 24 hrs after hydroxyethyl starch infusion; serum interleukin-6 concentrations remained at sham levels. Conclusions: Since the use of lactated Ringer's solution and hydroxyethyl starch after hemorrhage did not adversely affect cell-mediated immune functions, but produced salutary effects on macrophage functions, hydroxyethyl starch is a safe and beneficial resuscitation adjunct.