The effect of postischemically injected cyclohexyl adenosine has been studied in gerbils. The animals were subjected to 30 min of bilateral carotid occlusion. Fifteen minutes after ischemia, one group of gerbils received a cerebroventricular injection of 251 of 0.5 M solution of cyclohexyl adenosine. The second group of ischemic animals was injected with the vehicle. After injections, the animals were randomly divided into two groups. Survival of one group of animals was monitored for 10 days. The second group was killed 5 days after ischemia, and the brains were used for a qualitative and quantitative histological evaluation. At the end of the 10-day monitoring period, 53% of the cyclohexyl adenosine-injected and 10% of the vehicle-injected ischemic animals were still alive (P less than 0.01, logrank test). Morphological preservation of the hippocampus and striatum was considerably improved in the cyclohexyl adenosine-treated animals (P less than 0.001, Student's t test). The nature of the protective effect of cyclohexyl adenosine is unknown, but it is suggested that reduction of neurotoxic excitatory amino acid release may be involved.