In search for an effective treatment of human poisonings with ajmaline, a potent antiarrhythmic drug, the use of specific antibodies as neutralizing agents was explored in a preliminary animal model. For this purpose, New Zealand white rabbits were immunized with the antigen obtained after coupling the 17-hemisuccinate ester of ajmaline-21-acetate to bovine serum albumin, whereas other rabbits were immunized with the protein carrier only. While seven control rabbits receiving 0.625 mg/kg/min. ajmaline intravenously until death, died within 54.8 +/- 5.2 min. death was delayed until 137.7 +/- 15.5 min in seven ajmaline bovine serum albumin-immunized rabbits (p less than 0.001). Three bovine serum albumin-immunized rabbits behaved as controls. These results provide evidence that an immunological protection against ajmaline toxicity can be obtained in laboratory animals.