A study was conducted on 60 psychiatric patients to evaluate the reliability of a drug-exposure screening test based on gas chromatography/mass spectrometry analysis of hair samples for amitriptyline, and the possibility of using the hair concentrations of amitriptyline to monitor patients' therapeutic compliance. The qualitative test was found to be very reliable (sensitivity 93.3%; specificity 100%; positive and negative predictive values 100 and 93.8%) in assessing the consumer status of patients over a period of 2 months before analysis. Hair levels of amitriptyline ranged from 0 to 17.21 ng mg-1. A significant relationship (r = 0.563; P < 0.002) was found between the hair concentrations and the cumulative intake of amitriptyline over the studied period, but was not judged close enough to estimate one individual's therapeutic compliance. The results are discussed in the light of existing literature.