One-centimeter samples of hair from self-reported cocaine users were washed, rinsed with deionized water and methanol, and digested in an overnight solution. The digested samples were extracted with solid-phase extraction columns. This method is quantitative, requires a small sample of hair, and does not degrade the cocaine. There was little correlation between the concentration of cocaine in hair and self-reported drug use; the highest concentration was found in the hair of a moderate user and no cocaine was detected in the hair of a person who reportedly was a heavy cocaine user. The findings indicate that the concentration of cocaine in the hair is not solely determined by blood concentration of cocaine, but by other factors as well including type of drug, degree of ionization, and lipid solubility. Drugs may be absorbed into the hair from apocrine, sebaceous, or sweat gland secretions. 3 tables, 4 figures, and 32 references