A method for the titration of antistreptolysin O (ASLO) is described that is assumed to be more rapid than the methods applied thus far. The authors are drawing attention to the non-specificity of this method and propose to use PRESLO which is easy to prepare and admits of quantitative evaluation, for a control of this non-specificity. Correlation between the two reactions were established by the authors in 2137 sera which was expressed mathematically and made subject to subsequent statistical evaluation.