Surface-enhance Raman (SER) spectra of pyrazinamide (PZA), isoniazid (INAZ), and isonicotiamide (INCT) in silver sols have been studied over a range of solution concentration and pH. A linear calibration curve has been obtained for each of the sample molecules, and the lower limits of detection are estimated to be 5 ng for PZA and INAZ, and 10 ng for INCA. The variation of SER intensity with the sample solution pH is explained in terms of the charge of the sample species and the stability of the sols. The normal Raman and infrared spectra for the pure drug samples have also been collected, from which some vibration assignments for the molecules are given. The absorption behaviors of the molecules on the silver particle surfaces are also suggested.