The composition analysis found that pemoline was not the only component of the examined tablets (24 out of 1,076 tablets). In four kinds of tablets, pemoline was mixed with caffeine, piracetam (both are central nervous system stimulants), and acetylsalicylic acid. These three substances are widely available over-the-counter. They are frequently used as adulterants or additives in illegal street drug preparations. Acetylsalicylic acid was detected by a screening method that used high performance liquid chromatography with diode array detection. Pemoline, caffeine, and piracetam gave a single peak on the total ion current chromatogram; the pemoline peak height was very low compared to the two other components, despite having the highest concentration in the tablets. Pemoline peak height increased significantly, however, after warming up its methanol-water solution to 60 degrees C; whereas, the heights of piracetam and caffeine peaks remained almost constant, which indicates the better solubility of pemoline in a warm methanol-water mixture. The article concludes that pemoline in clandestinely manufactured tablets can be easily detected by gas chromatography/mass spectrometry and quantified by liquid chromatography/mass spectrometry. The most important stage of pemoline analysis proved to be its dissolving in the warm methanol-water solution. The article also advises that representative sampling is important when analyzing pemoline tablets that come from the narcotics market. 6 figures, 2 tables, and 7 references