Silver micro- and nanocrystaltites are prepared on porous Si substrates by immersion plating, and their activity toward SERS (surface-enhanced Raman scattering) is assessed. Scanning electron microscopy reveals a rough silver film containing randomly spaced dendritic structures. SERS spectra of Rhodamine 6G (R6G) and adenine are obtained using an 18-mW, 488-nm laser. The SERS signal from these analytes is dramatically improved by pretreatment of the silver-plated porous Si samples (Ag-PS) with a 1 mM mineral acid solution. Detection of R6G and adenine from 1 nM solutions is demonstrated, corresponding to (at most) 9 x 101 molecules in the experimental configuration used in the current study. Ag-PS samples that have been stored in air for 10 days still display high sensitivity. The presence of chloride either in the analyte solution or in the pretreatment solution is found to dramatically reduce the limit of detection for R6G.