[Asp1,p-fluoro-L-phenylalanine4]-angiotensin II ([pFPhe4]-AII) and [Asp1,p-fluoro-L-phenylalanine8]-angiotensin II ([pFPhe8]]AII) were synthesized by the solid-phase procedure in order to study their biological activity and 19F nuclear magnetic resonance (nmr) spectra. p-Fluoro-D,L-phenylalanine was resolved by enzymatic hydrolysis of N-trifluoroacetyl-p-fluoro-D.L-phenylalanine with carboxy-peptidase A. [pFPhe8]-AII is at least as potent as angiotensin II and [pFPhe4]-AII is an antagonist of angiotensin II in the rat oxytocic, the rat blood pressure, and the prostaglandin release assay. The 19F nmr spectra of [pFPhe8]]AII show that the C-terminal carboxyl has a pKa, of 3.1, that above pH 7 two conformations exist, and that the rate of exchange between these two conformations is slow on the nmr time scale. A conformational change with a pK of 6.1 is the most likely cause of the chemical shift change seen in the 19F nmr spectra of [pFPhe4]-AII.