This study investigates the ability of larvae and adult rover and sitter Drosophila melanogaster to detect and migrate towards the source of a fly medium attractant using larval plate assays and an adult olfactory trap assay. Allelic variation at the foraging locus which encodes a cGMP-dependent protein kinase (PKG) did not affect larval olfactory response in the larval plate assays. In contrast, adult males of the sitter mutant for(s2) exhibited an olfactory trap response (OTR) which was significantly greater than that of males of the wild type forR strain from which for(s2) was derived and further genetic analysis showed that this was attributable to the for(s2) allele. The olfactory responses of fbrR and for(s2) flies to three odours (propionic acid, ethyl acetate and acetone) in a T-maze assay was normal indicating that they did not have general olfactory deficits. The finding that adult flies who differ in their PKG enzyme activities differ in foraging behaviours and olfactory trap responses to yeast odours suggests that PKG signalling pathways are involved in olfactory related responses to food.