Colchicine-specific antibody (IgG(C] was tested in mice for reversal of colchicine toxicity. The mouse model was chosen because it reflects human pathophysiology in colchicine poisoning. IgG(C) was administered when at least 85% of colchicine was distributed in tissues. It resulted in a dramatic decrease in lethality from 85% (control group) to 10% (treated group). The decrease in toxic effects was confirmed by evaluating physiological parameters. The recovery of thermoregulation was very rapid in mice treated with IgG(C), while recovery in body weight was less marked. IgG(C) administration, therefore, decreases the intensity but may extend the duration of colchicine toxicity (reversible binding). The total neutralizing binding capacity of IgG(C) used was such that administered IgG(C) neutralizing binding sites were either 7 or 15% of the injected colchicine dose. In spite of this low neutralizing capacity the treatment was successful because of the ability of IgG(C) to buffer the amount of colchicine molecules on the critical slope of the dose-lethality curve.