Major Canby's points are well taken and we share his opinions. Our published studies dealt exclusively with the role of coagulase-positive penicillin-G-destroying staphylococci. It is entirely possible that other microorganisms may act in a similar fashion, as shown recently by Sabath and Finland (J. Bact., 85:314, 1963). This matter is currently under investigation in our laboratories. Although we have no final answers to this particular question, these studies have thus far convinced us that such microbial interactions are by far the most important causes of failure to eradicate group A hemolytic streptococci from the nasopharynx; microbial persistence, drug indifference, and conversion to "I" forms seem to be of little clinical significance in this setting.