Two Lysine mutants. one belonging to locus Lys-1 and the other belonging to locus Lys-2 were obtained by using Hydroxylamine as a mutagen Both the mutants showed vigorous heterocaryon formation between themselves. Of the 191 UV Induced Lysine mutants. 21 belonged to LYS-3. None to LYS-2. 34 to LYS-3 and 24 to LYS 4 LOCUS and 45 of LYS-5 Locus The results obtained by V V. and hyciroxyiamine have been found to differ in their mutation induced capacity of the five different loci controlling lysine biosynthesis in Neurospora crassa.