The olfactory receptor gene family is the largest gene family in the mammalian genome. There are approximately 1035 mouse olfactory receptors. Based on the phylogenetic analysis these receptors are categorized in 228 families, each sharing more than 40% sequence identity. Olfactory receptor family detects and distinguishes a huge number of odorants in a combinatorial fashion, meaning that one odorant can be recognized by many different receptors and that one receptor can recognize multiple odorant structures. In order to study chemical recognition and olfactory coding, we need to deorphanize olfactory receptors and define their molecular receptive ranges. Despite the availability of heterologous expressions systems, most mammalian olfactory receptors are still waiting to be deorphanized. Identifying olfactory receptor-ligand pairs is challenging for several reasons, including a) the large number of olfactory receptors that must be screened, b) the huge number of odorants, c) the heterogeneity in odorant structure and thus physicochemical properties, and d) the wide concentration range at which odorants may be active. So far, approximately 100 mouse olfactory receptors have been deorphanized. In the largest study so far, 52 out of 219 mouse olfactory receptors screened in vitro by Saito et al, were deorphanized using a selected set of 93 odorants. The full molecular receptive ranges of these receptors, however, have yet to be investigated. In order to measure odorant similarity/dissimilarity and to visualize odorant XAV939 position within in the huge odor space, Haddad et al. generated a multidimensional odor-map, where initially each odorant was represented by.1,000 molecular descriptors which were optimized to the 32 most salient descriptors. Similarly, Saito et al. analyzed the correlation between receptor responses and various molecular descriptors from a set of 93 odorants and found that 18 molecular descriptors are able to explain.62% of the variance in the mouse and human olfactory receptor responses. Thus, analyzing molecular descriptors of various odorants and placing them on the odor map enables us to measure the odor space representative of a particular olfactory receptor and to evaluate whether a receptor is broadly or narrowly tuned. Still, the heterogeneity of odorants makes in vitro screening strategies particularly challenging and labor intensive. Here we present another approach to study the molecular receptive range of olfactory receptors. We first applied virtual ligand screening to find additional ligands and to further characterize the molecular receptive range of MOR42-3. We employed two different scoring functions to estimate the strength of the receptor-ligand interaction, producing two lists of the top 20 candidate-binders. These 40 compounds were then tested in vitro for agonist, as well as for antagonist activity. From the first list we identified 10 agonists and 1 antagonist and from the second list we identified 9 agonists and 2 antagonists.