Cocaine hydrochloride, procaine hydrochloride, and lidocaine hydrochloride were obtained from Sigma-Aldrich Quimica, Spain. Glucose, sucrose, lactose, mannitol, starch, caffeine, priacetam, and potassium bromide were obtained from Merck, Germany. The infrared spectra were obtained with a Perkin-Elmer Model 1420 Infrared Spectrophotometer attached to a Perkin-Elmer Model 3600 Infrared Data Station. The equipment was attached to a IBM 80486 PC and a Pinwriter P22Q printer. Standard stock mixtures were prepared by mixing pure cocaine hydrochloride with 5 percent to 30 percent of the adulterant or diluent. Two regions of the IR spectra were used for the identification of the various components of the samples. The spectra of the mixtures of cocaine hydrochloride and several common adulterants (caffeine, procaine hydrochloride, lidocaine hydrochloride, and piracetam) and diluents (glucose, lactose, sucrose, starch, and mannitol) were recorded. Two regions were chosen in the infrared spectra: 1800- 1500 cm-1, which includes all the assayed adulterants, and 960- 860 cm-1, for sugars and polyalcohols. The display of the different spectra through the computerized program allowed the identification of the above-mentioned substances even at 5- percent concentration. 2 tables, 5 figures, and 12 references