The restoration of normal immune responses is a clinical goal in the severely immunosuppressed burn-trauma patient. The recently documented emergence of the suppressor system following major burns, however, dictates caution in the use of agents which stimulate immunologically competent cells. We describe an in vitro system, utilizing human peripheral lymphocytes, which accurately reflects the degree of immunosuppression of burned patients, and which can be used to predict the effect of immunologically active agents. Of a group of synthetic polyribonucleotides tested in this system, Poly I:C produced a significant favorable modulation in doses of 3.7 micrograms/ml. The most marked effect was noted in the subgroup of patients who eventually succumbed and in whom clinical modulation would be most advantageous.