1. A good correlation exists between histochemically judged and biochemically determined activity of alkaline phosphatase in the liver. 2. Normal localization of alkaline phosphatase in the human differs from that in the rat. 3. In Wistar rats normal localization is: low or no activity in bile canaliculi preferently in the peripheral part of the lobule. 4. Normal localization in the human is: moderate to strong activity in the sinusoidal wall, in the central and peripheral part of the lobule. 5. A relation exists between histochemical localization and serum value of alkaline phosphatase in rat and in human. 6. Raised activities at localizations where "normally" no activity is present, e. g. bile canaliculi in human, sinusoidal wall in rat, do correlate the best with raised serum activities.