The zonal distribution of cytosolic acetyl-CoA carboxylase, mitochondrial 3-hydroxyacyl-CoA dehydrogenase and 3-hydroxybutyrate dehydrogenase was studied in microdissected liver tissue. In fed male and female rats the activity of the lipogenic enzyme acetyl-CoA carboxylase was 1.6-times higher in the perivenous than in the periportal zone of the liver acinus. 3-Hydroxybutyrate dehydrogenase, which is involved in the formation of the ketone body, 3-hydroxybutyrate, exhibited a similar distribution pattern with a 1.5-1.8-times higher activity in the perivenous than in the periportal zone. In contrast, the activity of 3-hydroxyacyl-CoA dehydrogenase, the third enzyme in beta-oxidation, was about equally distributed between the periportal and the perivenous zone of the liver acinus. The results indicate a predominance of lipogenesis in the perivenous, mainly glycolytic zone of the liver acinus. Furthermore, these data support the hypothesis that beta-oxidation supplies energy for basic and anabolic processes like gluconeogenesis in the periportal zone, while it provides acetyl-CoA for ketogenesis besides energy for basic needs in the perivenous zone.