The synthesis of C5 labeled (+-)-5-[11C]methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten- 5,10-imine [(+-)-[11C]MK801] has been accomplished via alkylation of (+-)-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10-imine-N-t- butylformamidine [(+-)-5-des-methyl MK801 formamidine). The 11C labeling is accomplished by reaction of the anion of (+-)-5-des-methyl MK801 formamidine, generated with s-butyllithium, and [11C]methyl iodide.