We have quantitated the response of D. melanogaster to general anesthetics with a device, the inebriometer, that assays the fly's geotactic and postural behavior. When alleles of several loci that encode or regulate subunits of ion channels were compared with control stocks, several ion channel mutants clearly increased the anesthetic sensitivity of Drosophila. The effects were specific in that: a) for several alleles, genetic tests indicated that the anesthesia phenotype was due to the ion channel mutation and not to extraneous genetic differences between the stocks; b) a given ion channel mutation often affected the response to one anesthetic but not another; and c) the behavior of decapitated flies in the inebriometer indicated that the anesthetic phenotype of several mutants did not merely reflect a global change in the fly's physiology. These results provide support for the idea that ion channels are on the pathway(s) influenced by anesthetics and that different anesthetics use different pathways. They also provide perspective on the behavior of previously isolated mutations (har) that decrease the sensitivity of Drosophila to anesthetics in the inebriometer.