Although numerous cytokines, including interleukin (IL)-1, IL-8, and tumor necrosis factor, circulate in critically ill patients at risk for acute respiratory distress syndrome (ARDS), none clearly predict the development of the syndrome. We hypothesized that cytokines, such as IL-1ra, IL-10, and IL-4, which modulate inflammation, might contribute to or reflect the development of acute lung injury. Accordingly, serial levels of IL-1ra and IL-10 were measured in 77 patients who were identifed as being at risk for the development of ARDS. Initial IL-1ra levels were significantly higher (p < 0.0001) in the patients (7.82 [2.29-38.01] ng/ml) than in normal control subjects (0.24 [0.24-0.34] ng/ml) but did not predict the development of ARDS. Initial IL-1ra levels, however, were greater (p = 0.038) in the patients who died (31.95 [3.02-65.06] ng/ml) compared with survivors (6.61 [1.86-29.33] ng/ml). Similarly, IL-10 levels were increased in patients (155 [53.75-318.75] ng/ml) compared with normal control subjects (0 ng/ml) but did not predict the development of ARDS. Like IL-1ra levels, initial IL-10 levels were significantly higher (p = 0.005) in patients who died compared with survivors. IL-4 was not detectable in any of the patient plasma samples measured. Thus, modulators of inflammation are increased in patients at risk for ARDS who die, but do not predict the development of the syndrome.