Deferred consent, a new approach to the requirement for informed consent in clinical research, was used in a randomized clinical trial of brain resuscitation after cardiac arrest. Because patients were comatose and therapy had to be initiated immediately, traditional prospective consent usually could not be obtained. Using the deferred consent mechanism, family members were contacted after the first dose of experimental drug or placebo was administered and asked to consent for continued study participation. The vast majority of families were satisfied with the deferred consent mechanism. Their main concerns were about the safety of the experimental drug and whether the active drug or placebo was given. The concepts of randomization, blinding, and placebo-treated controls were generally not well understood. Although our experiences confirmed the impracticality of attempting to obtain traditional prospective consent in clinical resuscitation research, deferred consent was found to be a reasonable solution.