In connection with a study of chemically induced mutations, a number of 5, 6- dihydrocytosines have been synthesised by sodamide-catalysed ring-closure of the corresponding 2-cyanoethylurea and by amination of 4-thio-5, 6-dihydrouracils. Uv and ir spectra and p values of dihydrocytosine and its 1-methyl, 1-cyclohe
