Abstract Surface pressure-area per molecule isotherms have been obtained for N- tetradecanoly- l-alanine (myristoyl- l-alanine, l-MA), N- myristoyl- d-alanine ( d-MA) and their mixtures at the air/water interface at various temperatures to detect an eventual chiral discrimination occurring in N-acylamino-acid monolayers. It was found that the racemic mixture d-MA + l-MA exhibits, at a given temperature, a more expanded state than that of the pure enantiomeric one. Besides, the phase diagram of l-MA/ d-MA binary mixtures gives a positive azeotropy which means that the interactions between the two enantiomeric molecules ( l- d) are weaker than the interactions between the pure chiral molecules ( l- l or d- d), these interactions being at their minimum level when the mixture corresponds to the racemic composition. Any measurable difference in the interactions between two different chiral molecules is referred to as a diastereoisomer discrimination, compared to an enantiomer discrimination between two antipodes. This was checked through l-dimyristoylphosphatidylcholine l-DMPC)/ l- and d-MA mixed monolayer studies. No difference was observed in the phase diagram of binary mixtures of l-DMPC/ l-MA and l-DMPC/ d-MA, which shows that, in such systems, diastereoisomer interactions cannot occur because of the relative inaccessibility of the phospholipid chiral center.