Genetical study of olfactory response to ethyl alcohol (8 per cent) has been carried out on inbred lines extracted from a natural population using biometrical and chromosome analyses. A full diallel analysis was made in seven endogamic lines (3 high, 3 low and 1 intermediate in response values). Our results show a highly significant (P less than 0.001) additive component of variance and a less significant (P less than 0.05) directional dominance component suggesting overdominance and some endogamic depression. No significant maternal or reciprocal components of variation appear in our population. Two chromosome substitution assays among 3 inbred lines of extreme olfactory response add up information to the results of diallel analysis. The differences in response are due to chromosome III with an additive effect highly significant (P less than 0.001) in both studies. The other major chromosomes do not show any effect themselves but some interactions with chromosome III are significant. They can explain the directional dominance that we find in the diallel study. Analysed olfactory variation in response to ethanol can be considered as unspecific in relation to various chemical compounds.