Intracerebroventricular (i.c.v.) injection of streptozotocin has been introduced as a means to inhibit glucose utilization in the rat brain, and to induce changes in neurotransmitter systems and behavior which resemble those seen in Alzheimer's disease. In this study, enzyme activities previously investigated in Alzheimer's disease (peptidases, dehydrogenases and acetyltransferases) were measured in the septum and hippocampus of control and streptozotocin-treated rats. Streptozotocin-treated rats receiving acetyl-l-carnitine were also included in the experiments, to assess possible neuroprotective effects of this substance. All enzyme activities in the septum were affected by streptozotocin, with the exception of choline acetyltransferase activity. By contrast, choline acetyltransferase activity was the only enzyme activity affected in the hippocampus. The weight of the septum was reduced in streptozotocin-treated animals. These findings indicate that i.c.v. injection of streptozotocin causes septal damage and enzymatic changes that do not closely resemble those seen in Alzheimer's disease, which are more specific. Acetyl-l-carnitine partly prevented this damage, as reflected by an attenuation of the streptozotocin-induced decrease in hippocampal choline acetyltransferase activity. This finding indicates that streptozotocin-treated rats may be valuable to test possible neuroprotective effects of drugs.