232 cultures were plated on Ludlam''s medium (Monthly Bull. Ministry of Health, 8:15. 1949) and on staphylococcus medium no. 110 (Trans. N.Y. Acad. Sci. 9:52. 1946). Large black colonies on the former and pig-mented colonies on the latter were tested for blood-coagulating power. There was agreement in the number of blood-coagulating staphylococci (83%); 5% showed 1-10 colonies on the former but none on the latter; 6% of colonies on the former did not clot blood; 4.7% of the cultures showed 2(1 culture), 6 (2 cultures), many (3 cultures), moderate number (1 culture) and a very large number (1 culture) on no. 110 but none on Ludlam''s medium. In view of these failures, Ludlam''s medium is not reliable when used alone.