Animals must efficiently detect and process stimuli, then tune behavioral output according to dynamic physiological demands. To achieve this, the nervous system uses neuromodulators, such as serotonin (5-HT), to modify the excitability and synaptic efficacy of individual neurons based on the animal’s current state. Neuromodulation, therefore, can result in changes in lateral interactions within the network and shape the direct output from the network. For instance, 5-HT enhances odor-evoked responses of projection neurons (PNs) and enhances pre-synaptic inhibition of olfactory receptor neurons (ORNs) by local interneurons (LNs) within the antennal lobe (AL) of D. melanogaster. However, the effect of a neuromodulator on an individual neuron is dictated by the cognate receptor-type expressed by that neuron. Therefore, to understand the mechanistic basis for neuromodulation, the functional identity of the neurons that express each neuromodulator receptor within a network must be determined. This will allow the separation of the effects of a neuromodulator on a single neuron from the consequences of modulating the input that a neuron receives. Therefore, we have used immunocytochemistry and T2A-GAL4 transgenic animals driving the expression of GFP to determine the neuron type within the AL of D. melanogaster that express the five 5-HT receptors (5-HTRs). The T2A-GAL4 lines act as a direct reporter for 5-HTR translation (“protein-trap”) by decoupling GAL4 from the nascent 5-HTR mRNA during translation. Using immunocytochemistry, we determined the cell type (i.e. ORN, PN, LN, etc.) and transmitter content of each 5-HTR producing cell in the AL. Each 5-HT receptor are expressed by distinct functional populations of neurons suggesting that 5-HT targets distinct features of olfactory processing within the AL. In general, the inhibitory 5-HT receptors are expressed by inhibitory neurons including distinct subpopulations of LNs and GABAergic PNs, while the excitatory 5-HT receptors were expressed by ORNs and cholinergic PNs. This suggests that within the AL, the effects of 5-HT on olfactory processing are mediated by a combination of network-wide disinhibition and glomerulus specific enhancement. .