The diffusion coefficients (D) of tert-butyloxycarbonyl-L-phenylalanine (Boc-Phe) in Merrifield network polystyrene gels, used as a solid-phase reaction field have been determined as a function of the amino acid concentration over the temperature range from 30 to 50 degreesC by means of the H-1 pulsed-field-gradient spin-echo NMR method. From these experimental results, it was found that the D value of Boc-Phe in DMF-d(7) solution, in DVB 1 and 2% cross-linked network polystyrene gels depends on the amino acid concentration. The D value of BocPhe-Cs(tert-butyloxycarbonyl-L-phenylalanine cesium) salt in the solid-phase reaction field under chemical reaction was determined at 50 degreesC. Further, it was found that the D value depends on the NMR observation time, that is the applied two field-gradient pulse interval. Details of its analysis were discussed.