Background - Previous studies have investigated toxicity inhibition of optically active compounds by potentized preparations of their enantiomers. It was hypothesised that inhibition of toxicity may be stereospecific. This paper presents 2 studies investigating stereoisomer potencies in terms of their ability to counteract toxicity of the (−) stereoisomer. The stereoisomers used were (−)-trans-(1S,2S)-U-50488 HCl and (+)-trans-(1R,2R)-U-50488 HCl.Materials & methods - Designs were prospective, blind, randomised, intention-to-treat and compared the efficacy of 2 indistinguishable treatments. The outcome was the difference in survival. Potency ‘chords’ consisting of 4th, 12th and 30th approximately centesimal dilutions were prepared, representing concentrations of 1.08 × 10−10 M. One study compared inhibition of (−)-U-50488 toxicity injected ip at the estimated LD50 into male ICR mice, treated with a potency chord of the same stereoisomer, with control (‘isopathic’ study). The other study compared inhibition of toxicity by potency chords made from the stereoisomers (+)-U-50488 and (−)-U-50488 (‘enantiomer’ study), Treatments were administered orally on 11 occasions: twice before and nine times after ip injections.Results - The isopathic study did not yield a significant result. In the enantiomer study, comparison of isopathy with enantiomer potency treatment showed a highly significant difference odds ratio 1.97 (95% CI: 1.23–3.14).Conclusion - We conclude that enantiomeric potencies are superior to identically produced isopathic potencies, in inhibiting toxicity of (−)-U-50488 HCl. Homeopathic inhibition of toxicity may be stereospecific.