New results are presented concerning insertion of two antibiotic ionophores Lasalocid and Monensin as sodium salts (LAS-Na, MON-Na) in biomimetic membranes. Langmuir films of Dipalmitoylphosphatidylcholine (DPPC) have been used as model systems. Evolution of the compression isotherms has been investigated below the gel - liquid crystal phase transition, between the ambiant and temperatures approching physiological conditions, not only for the pure antibiotics but also for the antibiotic - lipid mixtures, the molecular ratio ρ antibi-otic/lipid equal to 0.1. In the mixed films with LAS-Na, the antibiotic molecule is well maintained by the film also when raising the temperature, whereas MON-Na is expelled above the low pressure region. The results are discussed and compared with effects produced in model systems of bilayers submitted to similar temperature variations.