PVP-protected silver colloids were prepared by gamma-irradiation and chemical reduction method. Surface-enhanced Raman scattering (SERS) spectra of sodium benzoate and 4-picoline in Ag colloids prepared by gamma-irradiation were recorded. The SERS spectra of sodium benzoate were successfully recorded in Ag colloids, whereas the Raman spectra did not appear without Ag colloids. The Raman spectra of 4-picoline were not detected without Ag colloids, while the SERS spectra of 4-picoline were increased by adding Ag colloids. The carboxylate group of sodium benzoate and N donor of 4-picoline were adsorbed on the surface of Ag nanoparticles. (c) 2004 Elsevier B.V. All fights reserved.