Recent laboratory endeavors have been primarily concerned with determining the effects of chronic ethanol ingestion on cerebral RNA metabolism within the inner mitochondrial membrane (IMM). Toward this goal, a series of experiments were carried out by determining the RNA and protein synthetic activity of the organelle. Brain mitochondria actively incorporated [5-3H]orotic acid into RNA under in vivo conditions. In addition, data showed that a major portion of the radioactivity present in the cold TCA insoluble residue from labeled intact mitochondria could be recovered in the digitonin treated purified IMM fraction. Maximum incorporation of [5-3H]orotic acid into RNA took place within 24 hrs followed by a rapid decline in activity on the 5th day of the pulse in both 'control' and 'ethanol' ingesting rats. Data revealed that ethanol ingestion affected the degree of incorporation of labeled RNA precursor into the mitochondrial RNA fraction. The observed effect was in the form of inhibition and was dependent on the duration of the initial pulse. Thus, while at earlier time points a decreased incorporation of the precursor into mitochondrial RNA was obtained in the ethanol imbibing rats, the inhibition was not observed when the pulse time was extended to 5 days. Such results indicate the possibility of a rapid turnover rate for the brain mitochondrial RNA with the 'ethanol' group having a faster rate of turnover when compared to the 'control' group.