WHAT ARE THE limits of religious freedom? The Supreme Court will take up that recurrent question on November 1 when it hears arguments in a case involving O Centro Espirita Beneficiente Uniao Do Vegetal, a small sect that blends Christianity with South American spiritism. As a central act of their faith, UDV members ingest a tea called hoasca, brewed by mixing two plants unique to the Amazon basin (uniao do vegetal is Portuguese for "union of the plants"). They believe that hoasca connects them to God.

This practice has landed the UDV--which has 8,000 members in Brazil and 135 in America--in trouble with the U.S. government. Hoasca contains a small fraction (just over one hundredth of 1 percent) of a naturally occurring hallucinogen called dimethyltriptamine (DMT), which is prohibited under federal drug laws. This amount, although small, is sufficient to alter the drinker's state of consciousness. The UDV imported its hoasca from Brazil until May 1999, when customs officials confiscated a shipment and federal prosecutors threatened the group with criminal charges.

The UDV sued the government in federal court, alleging that it had violated the First Amendment's "free exercise of religion" clause and the 1993 Religious Freedom Restoration Act. After a two-week hearing, the judge ordered, pending a full trial, that the government allow the UDV to import and use hoasca subject to controls designed to prevent its spread to a broader market of recreational users. After the court of appeals upheld this injunction, the government successfully petitioned the Supreme Court for a review.

The case of Gonzales v. UDV raises a long-standing question: when a general law enacted for a legitimate purpose, like the drug law, conflicts in a particular case with a religious practice, should the law give way and exempt the practice? The Supreme Court has vacillated on this issue.

In 1879, holding that Mormons could be prosecuted for engaging in polygamy, the court reasoned that government cannot "excuse ... [illegal] practices" on the basis of religious conscience, lest "every citizen ... become a law unto himself." But in the 1960s and '70s the court, emphasizing the fundamental nature of free-exercise rights, held that government cannot substantially restrict those rights, even when enforcing a general law, unless it can show "interests of the highest order" that would be undermined were an exemption granted.

In 1990 the court changed course again, in another case involving sacramental drugs: the ritual ingestion of peyote from cactus plants by members of the Native American Church. The majority in Employment Division v. Smith held that in most cases, a "neutral law of general applicability" can be applied to religious conduct no matter how serious the burden it imposes, and even if it serves no strong interest whatsoever. The court's opinion, written by Justice Antonin Scalia, called an exemption from an otherwise valid law a "constitutional anomaly" and said that judges lack competence to balance religious interests against social interests and so determine which practices to exempt.