Methotrexate-3H was accumulated in vitro against a con centration gradient by the rabbit choroid plexus. This accumu lation was energy dependent, inhibited by metabolic inhibitors, and exhibited self-saturation and competitive inhibition. Several folie acid analogs with a 4-amino group were inhibitors of this accumulation, while folie and folinic acid, compounds which do not contain a 4-amino g...
