Good chiral recognition of diketopiperazines has been obtained with a receptor that combines a xanthone with a phosphonamide as an asymmetric group. Silicagel plates impregnated with an enantiomerically pure diketopiperazine provide an easy and effective way to resolve the receptor racemic mixture. The strong (R,R. R) complex yields a spot with a larger R-f probably because the complex is less polar than the free receptor.