Mutagenic efficiency and effectiveness is an important factor for the selection of a mutagen for a mutation breeding program. The mutagenic efficiency gives an idea of the proportion of mutation on relation to the other associated undesirable biological effects such as lethality, sterility and meiotic aberrations while mutagenic effectiveness is a measure of the frequency of the mutation induced by unit dose of mutagens. The usefulness of any particular mutagen in crop breeding depends not only on its mutagenic effectiveness but also on the mutagenic efficiency of the mutagen. Studies on mutagenic efficiency and effectiveness of chemical mutagen sodium azide (NaN3) on variety Pusa mustard 21 of Indian mustard have been reported. | Studies on mutagenic efficiency and effectiveness of sodium azide on Indian mustard in M2 generation