The adsorption of N-methylacetamide and of L-arginine on apatitic phosphates has been studied by infrared spectroscopy. During the initial adsorption, the bands of adsorbed N-methylacetamide indicate the presence of the trans form attached to surface cations via the carbonyl group. The position of the amide I band is found to give a linear correlation with q/r for apatitic cations (where q is the charge and r the radius of a cation). At higher amounts of adsorbed amide, hydrogen bonding arises either from the self-association of amide molecules or from the binding of these to the surface phosphate anions. L-Arginine can be adsorbed through the groups containing NH bonds or through the carboxyl group. Infrared spectra of calcinated samples as well as the Ca/P ratio determinations point out that a substitution of L-arginine positive ions for surface cations takes place upon adsorption of this amino acid on apatitic calcium phosphate.