Many quantitative trait loci (QTLs), including those for ethanol-related tr
aits, have been mapped in the mouse. In light of rapidly developing tools a
nd resources, we briefly review the strategy for identifying the genes unde
rlying these QTLs. We note that positional cloning will soon be a matter of
testing candidate genes rather than discovering genes; therefore, we descr
ibe a "congenic test'' to support that a candidate gene is indeed a QTL. Co
nsidering the rapid development of congenics and mutants, we also identify
four areas of investigation-phenotypes, ethanol specificity, environment, a
nd gene interactions-that might be exploited during the course of positiona
l cloning to gain insights into QTL pathways. In particular, we note that m
ultiple mutants of nearly every major neurotransmitter pathway have now bee
n made. These mutants are not only useful for phenotypic tests, but also co
uld be used to conduct "gene dependence" tests of QTLs. We also consider po
tential applications for the very recently developed ability to clone mice.