The olfactory system discriminates among thousands of odorants. Odor transduction occurs in the chemosensory cilia of olfactory receptor neurons (ORNs). Odorants induce excitatory or inhibitory responses, characterized by increases or decreases in firing rate, respectively. Both response types can be generated by a single ORN and are thought to involve G-protein coupled odor receptors that trigger a cAMP cascade, activating cyclic nucleotide gated-channels. A Ca²⁺ influx through such channels activates depolarizing Ca²⁺-dependent Cl^– channels, in the first case, and hyperpolarizing Ca²⁺-dependent K⁺ channels, in the second situation. We investigated the presence of scaffolding proteins in the olfactory epithelium, because such proteins could be involved in the organization of the transduction apparatus. This would have important physiological implications. Scaffolding proteins like MAGuKs (membrane-associated guanylate kinase homologs) contain PDZ (PSD95/Dlg/ZO homolog), SH3 (Src homolog) and GuK (Guanilate kinase homolog) domains that mediate protein-protein interactions. The PSD95/SAP90 family of MAGuKs has 4 homolog members: PSD95/SAP90, SAP97/Dlg, SAP102/NE-dlg and Chapsyn110/SAP93. We isolated a subcellular fraction of olfactory cilia, as indicated by specific markers. Epithelia were obtained from adult rats killed by an anaesthetic overdose (pentobarbitone 60 mg/Kg ip), according to the guidelines of the Ethics Committee of the University of Chile. Western blots showed several bands between 33 and 120 kDa, reactive to an antibody against PDZ domains of the PSD95/SAP90 family. These bands were present in the ciliary fraction, and some of them were absent in forebrain homogenates (positive controls), suggesting that they may correspond to new isoforms or to postranslationally modified proteins of the PSD95/SAP90 family (5 times). When we tested specific antibodies against each member of the PSD95/SAP90 family, PSD97 was detected (twice), whereas an anti-SAP102 antibody revealed a band with a smaller molecular weight than in the forebrain (4 times). In RT-PCR experiments with cDNA from the olfactory epithelium (twice), we used specific primers for several regions of neuronal SAP102. The results support the presence of a SAP102 sequence with deletions in the HOOK region connecting the PDZ3 and SH3 domains. The deletions are either in exon 2 or 14 and may account for the lower molecular weight species in the Western blots. Our results suggest that scaffolding proteins are present in olfactory cilia, where they may have a key role in transduction.