Abstract: We report here preliminary results of an attempt with a cell hybrid which when inoculated on the stem of the tomato plant, produced crown galls (tumors) possessing nitrogenase activity (by acetylene reduction test) under aerobic conditions. This is done by cell (protoplast) fusion between the parent strains of Agrobacterium tumefaciens (Penr, Ti) and Azotobacter chroococcum (Pens, Nif+). The crown galls caused by this hybrid on the tomato stem appear to possess N2 ase activity under aerobic conditions (0.05–0.2 atm O2). The tumors reduce 14n M of C2H2 per hr per gm fresh weight (table 3) in these preliminary experiments. Further experiments are still in progress. We gratefully acknowledge Prof. P. S. Tang for his instructive suggestions and encouragement in our work.