Single P-element (P[lArB]) insertional mutagenesis of an isogenic strain was used to identify autosomal loci affecting odor-guided behavior of Drosophila melanogaster. The avoidance response to benzaldehyde of 379 homozygous P[lArB] element-containing insert lines was evaluated quantitatively. Fourteen smell impaired (smi) lines were identified in which P[lArB] element insertion caused different degrees of hyposmia in one or both sexes. The smi loci map to different cytological locations and probably are novel olfactory genes. Enhancer trap analysis of the smi lines indicates that expression of at least 10 smi genes is controlled by olfactory tissue-specific promoter/enhancer elements.