Previous toxicity testing with fathead minnows (Pimephales promelas) indicated that some unsaturated acetylenic and allylic alcohols can be metabolically activated, via alcohol dehydrogenase, to highly toxic alpha, Beta-unsaturated aldehydes and ketones or allene derivatives. Although several in vivo and in vitro toxicological and biochemical endpoints can differentiate these alcohols by toxic mechanism, the use of stereoelectronic molecular descriptors to discriminate these toxicants, and subsequently to predict potency, has not been previously attempted. Exploration of several descriptors indicated that soft electrophilic characteristics of acetylenic or allylic moieties in the suspected metabolites unambiguously discriminated reactive and narcotic toxicants. (Copyright (c) 1993 VCH Verlagsgesellschaft.)