1. After i. v. injection in rats, harmine and harmaline were distributed in the organism within a few seconds. In spite of the close chemical relationship, both alkaloids revealed significant pharmacokinetic differences. 2. Highest concentrations occurred for harmine in the lung and for harmaline in the kidney. The uptake into brain was for harmaline slower than for harmine. The rate of elimination was in general smaller for harmaline than for harmine. 3. Harmaline was excreted into chymus and urine to a greater extent than harmine. 4. The binding to proteins of rat plasma was 94.5% for harmine and 52% for harmaline. Concentrations of free drug in plasma water were used to assess the binding to various tissues. 5. The extent of tissue binding and the rate of its development were different for both drugs. 6. The duration of tremor and the strength and decline of bradycardia were determined to compare the distribution of the drugs with their effects. 7. The drug concentration (in brain and heart) at the termination of the effect (tremor and bradycadia) was used as a parameter connecting the pharmacokinetic and the pharmacodynamic events.