[(18)F]altanserin is the preferred radiotracer for in-vivo labeling of serotonin 
2A receptors by positron emission tomography (PET). We report a modified 
synthesis procedure suited for reliable production of multi-GBq amounts of 
[(18)F]altanserin useful for application in humans. We introduced thermal 
heating for drying of [(18)F]fluoride as well as for the reaction instead of 
microwave heating. We furthermore describe solid phase extraction and HPLC 
procedures for quantitative determination of [(18)F]altanserin and metabolites 
in plasma. The time course of arterial plasma activity with and without 
metabolite correction was determined. 90 min after bolus injection, 38.4% of 
total plasma activity derived from unchanged [(18)F]altanserin. Statistical 
comparison of kinetic profiles of [(18)F]altanserin metabolism in plasma samples 
collected in the course of two ongoing studies employing placebo, the serotonin 
releaser dexfenfluramine and the hallucinogen psilocybin, revealed the same 
tracer metabolism. We conclude that metabolite analysis for correction of 
individual plasma input functions used in tracer modeling is not necessary for 
[(18)F]altanserin studies involving psilocybin or dexfenfluramine treatment.