The disappearance of antibodies to myotoxin a from the bloodstream in mice was measured with a specific ELISA over a ninety-six hour period in the presence and absence of myotoxin a. A gradual disappearance of antibodies to myotoxin in the absence of toxin was observed during the 96 hr sampling period, although antibodies were still detectable at 96 hrs. However, in the presence of myotoxin a very rapid decrease of antimyotoxin occurred. When antiserum injection was followed by myotoxin injection (5 min. later) the decline in antibodies was immediate and no antibodies could be detected 30 min. after the antiserum injection. When antiserum was injected either immediately or 30 min. after toxin, antibody levels declined sharply and were non-detectable 1 hr. after antiserum injection. These results have clinical significance since they indicate that antimyotoxin can still bind the toxin, even when administration of the antiserum is delayed for 30 min. after injection of the toxin. Multiple injections of antiserum may be required to maintain a neutralizing level of antiserum.