Streptococcal nuclease B is an extracellular product that is produced by a large number of strains of Streptococcus pyogenes and which elicits antibodies that have probed to be a useful index of streptococcal infection. The measurement of antistreptolisin O and antistreptococcal nuclease B (antideoxyribonuclease B) is a better criteria in the establishment of a diagnosis of streptococcal infection. An obstacle to this strategy in the past was the difficulty of preparing nuclease B antigen homogeneous with respect to its nuclease activity. The present report details a further simplified procedure for isolation of nuclease B by ion exchange - on DEAE sepharose CL-6B, wich facilitate the ready ,availability of this antigen.