AbstractThis article reports on the comparison of self-reported cocaine use with urinalysis outcomes and radioimmunoassay of hair samples for cocaine. The data is based on a voluntary sample of approximately 300 arrestees, tested and interviewed anonymously. The study reports high rates of request compliance for both urine and hair samples, and affirms a relatively high degree of underreporting of cocaine use. Radioimmunoassay of hair appears to detect considerably larger degrees of cocaine use than are detected by urinalysis. The differential rates of detection between hair and urine are less dramatic in subjects who appear to be high rate users.