The halothane gene (HALn) has beneficial effects on lean yield, and adverse effects on stress susceptibility, meat quality and litter size. The gene appears additive for lean content, but largely recessive for halothane sensitivity and other traits. Manipulating the frequency of the gene can lead to a worthwhile improvement in performance. At present, complete elimination of the gene requires expensive test matings, and a cheap and accurate method is needed for detecting heterozygotes. Reaction to the muscle relaxant succinylcholine was therefore investigated as a possible method of distinguishing the heterozygote (Nn) from the normal homozygote (NN).