Distribution of Amethopterin in Normal Mouse Tissues Following Intravenous Injection.

The concentration of ametho-pterin in the serum, liver, kidney, spleen, lungs and muscle of normal mice at intervals following intravenous injection of 0.5 mg/kg has been ascertained. 2. The relative concentrations of amethopterin in the tissue appeared to parallel the folic acid and CF content viz. liver, kidney, and spleen in descending order. No significant quantity of amethopterin was found in the lungs or muscle. 3. Ametho-pterin-like activity was found to be still present in the liver and kidney in relatively large quantities 24 hours after injection although the serum level had reached or approximated zero in 4 hours.