Research was conducted on the plants grown from confiscated seeds and that were quantified by gas chromatography. The results confirmed the validity of the toxicity classification of cannabis plants proposed by Small and Cronquist. Flowering stage of the plant was shown to be the critical one to estimate THC content. Cannabis with a THC over 50 percent and 0.3 percent are the most toxic and most often used for drug abuse, while that less than 50 percent is a low intoxicant that can be used in oil and rope manufacture. The parameters observed in the study permit prediction of toxicity levels in even young cannabis plants. 3 tables and 4 references. (Author abstract modified)