A portable near infrared spectrometer was applied to the presumptive identification of psychotropic drugs based on library searching. Data-treatment methods (mathematical pretreatment and library search algorithm) were examined on the basis of differentiation ability. The optimized mathematical pretreatment was a standard normal variate followed by the 2nd derivative. The correlation coefficient showed the best differentiation ability in the library search algorithms. Optimized data-treatment was effective for minimizing the effect of particle size on identification. The optimized data-treatment methods were validated by the spectra of psychotropic substances (n = 120). Identification criteria for the psychotropic drugs were decided on the basis of the results of the validation. As a consequence, 8 out of 11 forensic samples containing psychoactive substances were able to be positively identified. Thus, the portable near infrared spectrometer with optimized data-treatment processing is a useful tool for rapid screening and presumptive identification of seized materials. (C) 2014 Elsevier Ireland Ltd. All rights reserved.