Lasalocid A (LasNa), a common antibiotic in veterinary medicine, is a polyetheral ionophore, disrupting cation equilibria through the cell wall. By means of circular dichroism (in the UV and in the near-IR), paramagnetic NMR, and with the aid of the program PERSEUS, we determined the solution geometry of the 1:1 Las-Yb3+ complex in CD3CN and CDCl3, following a protocol similar to the one successfully used for the anthracycline-metal adduct. The resulting structure is in full agreement with the expectation of the ligand wrapping around the cation in a horseshoe shape. The oxygen atoms participate in the coordination either through a direct, first sphere, or a longer range interaction.