In the study, analytical conditions for the determination of selected cannabinols by GC-FID and HPLC-UV methods were optimised and an attempt was made to develop a determination procedure for these compounds in hair. Application of MTBSTFA derivatisation of cannabinols in the GC-FID procedure resulted in much lower limits of detection. For hair sample preparation in the HPLC-UV procedure, ultrasonic-assisted extraction (UAE) and dichloromethane as an extrahent were chosen. The best chromatographic separation of cannabinols was achieved by HPLC-UV in isocratic elution with acetonitrile and 0.05 mmol/dm3 formic acid (75:25, v/v). For the developed procedure which utilised UAE-HPLC/UV, the evaluated limits of detection in hair were: 3.4 µg/g for THC, 0.2 µg/g CBN, 0.5 µg/g CBD and 0.4 µg/g for THC-COOH. The procedure was applied to the determination of cannabinols in authentic hair samples (n = 12), and the average concentrations in 1 g of hair were: 3.4 µg THC (n = 1);  1.4 µg CBD (n = 7); 0.5 µg CBN (n = 11) and 2.1 µg THC-COOH (n = 12).