Mutagenicity inhibition of MNNG*, NFAA* as well as of nitrovin by ascorbic acid was observed. The influence of ascorbic acid on these compounds was parallelly studied also by spectroscopy. Mutagenicity inhibition was characterized by SOS chromotest. Inhibition degree was evaluated quantitatively introducing the coefficient of inhibition. The influence of ascorbic acid was expressed most markedly in MNNG. It has been found that the decrease of mutagenicity should be mainly caused by acceleration of MNNG decomposition by ascorbic acid.