Twelve advanced lines of mustard (Brassica juncea L.) were evaluated for response to treatment with Azospirillum brasilense in yield and a few components. Two lines gave yield increases with concomitant increases in nitrogenase activity and Azospirillum population. In general, there were desirable and significant correlations between plot yield, nitrogenase activity and log, (Azospirillum population). The results point to the possibility of utilizing genotype-dependent response to Azospirillum in breeding programmes and also for exploring new avenues of Azospirillum-based cultural practices in sustaining improved productivity