Methylnitronitrosoguanidine

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

MNNG is a probable human carcinogen listed as an IARC Group 2A carcinogen.

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