A 1H n.m.r. study of some methoxy-, methylthio- and chloro-N-methyl-purines and imidazo[4,5-c]-pyridines revealed that the signal due to the N-methyl group when present in the six-membered ring occurred at lower field than when present in the imidazole ring. The methylation of 2-,6-and 8-methoxypurines with diazomethane, and metatheses of chloro-N-methylpurines each to methoxy-N-methylpurines are described.