Solutions of LiPi and LiClO4 in nitromethane were studied by conductance at 25-degrees-C in the concentration range 0-10(-2) mol l-1. Although the dielectric environment is the same, the conductometric behavior of these two electrolytes is quite different : LiPi is almost non-conducting whereas LiClO4 behaves like a normal electrolyte. The analysis of the conductance data gives ion pair association constants of the order of 10(6) for LiPi and 10(2) for LiClO4. The results are discussed in terms of specific ion-ion and ion-solvent interactions related to the molecular details of the anions and the solvent molecules. One-to-one complexes between 15-crown-5 and the lithium ion were observed, adding the macrocyclic ligand to the systems. A dramatic increase in the conductance of both electrolytes in the presence of 15-crown-5 was also observed. The overlap of the complexation process and the ion-pair process is discussed.