IN the course of work on auto-antibodies in patients suffering from multiple myeloma marked fibrinolytic activity was discovered in one of the sera. Further investigation revealed that it was contaminated with two kinds of bacteria, one a member of the genus Pseudomonas, the other a strain of Streptococcus faecalis. The role of Pseudomonas was shown to be the conversion of glucose to gluconic acid. In the presence of the latter compound S. faecalis would produce the fibrinolytic agent.