A procedure to detect illicit drug use by testing hair is being adopted at some schools, primarily private ones. Civil liberties groups, which oppose the tests, argue that they are inaccurate.

• Hair testing is based on the premise that drugs ingested in the body travel through the bloodstream and are deposited in hair follicles roughly in proportion to the amount of the drug taken.

• Since hair grows at the rate of half-an-inch a month, the test uses the inch and one-half closest to the scalp to detect drug use during the latest 90 days.

• Questions have been raised, however, as to whether drug molecules bind more to coarser black hair than to lighter hair and whether passive exposure to marijuana or other smoked drugs could produce a false positive.

Private schools can make drug testing a condition of enrollment without inviting lawsuits.

But public schools cannot Yet two public school principals in New Orleans want to initiate hair tests. The American Civil Liberties Union of Louisiana has warned that it would file suit if testing is implemented.

Source: Christopher S. Wren, "Hair Testing by Schools Intensifies Drug Debate," New York Times, June 14, 1999.