A number of studies have suggested that the inflammatory and chemotactic autocoid platelet activating factor (PAF), together with various cytokines, plays an important role in the pathophysiology of trauma, sepsis, and shock. However, little is known about PAF's contribution to the immunosuppression associated with hemorrhage. The aim of our study was, therefore, to determine if the use of a PAF-antagonist following hemorrhage has any salutary effects on splenocyte lymphokine production. To study this, mice were bled to and maintained at a mean arterial pressure of 35 mm Hg for 60 min. The mice were then segregated into three groups and were resuscitated with shed blood plus lacrated Ringer's solution (2 × the volume of shed blood), containing either a potent PAF-antagonist (Ro 244736, a thienodiazepine) in dimethyl sulfoxide (DMSO) or DMSO-vehicle. Sham-operated mice received either DMSO-vehicle in saline or saline alone. Twenty-four hours thereafter the animals were sacrificed and splenocyte cultures established and stimulated for 48 hr with Con A (2.5 μg/ml). Supernatant lymphokine levels were determined by bioassay. The cellular release of interleukin-2 and -3 (IL-2 and IL-3) by splenocytes was significantly depressed in the nontreated or vehicle-treated hemorrhaged animals compared to shams. Treatment with the PAF-antagonist Ro 24-4736 restored IL-2 and IL-3 release values to levels comparable to those of the sham-operated animals. Thus, (1) PAF appears to play a significant role in hemorrhage-induced immunosuppression and (2) the use of a PAF- antagonist to uncouple the PAF-generated feedback loops prevents the depression in splenocyte function following hemorrhage. We propose that PAF- antagonists may be useful in the treatment of hemorrhage-induced immunodepression. © 1995 Academic Press, Inc.