Methylnitronitrosoguanidine (MNNG[2] or MNG, NTG when referred to colloquially as nitrosoguanidine[3]) is a biochemical tool used experimentally as a carcinogen and mutagen.

[1] It acts by adding alkyl groups to the O6 of guanine and O4 of thymine, which can lead to transition mutations between GC and AT.

These changes do not cause a heavy distortion in the double helix of DNA and thus are hard to detect by the DNA mismatch repair system.

In organic chemistry, MNNG is used as a source of diazomethane when reacted with aqueous potassium hydroxide.

[5] MNNG produces diazomethane, a known methylating agent of DNA and other substrates, in basic aqueous solutions, and nitrous acid, a mutagen, in acidic solutions.