7-Methylguanosine (m7G) is a modified purine nucleobase. It is a methylated version of guanosine and when found in human urine, it may be a biomarker of some types of cancer. It also plays a role in RNA as blocking group at its 5´-end. 7-Methylguanosine may be used to characterize and study the metabolism of naturally occurring methylated guanosines in RNAs.