Sixteen cases of adverse effects due to a new health-food product, gamma-hydroxybutyrate (GHB), were reported to the San Francisco Bay Area Regional Poison Control Center in the 5-month period from June to October 1990. Cases have also been reported in eight other states. Adverse effects included coma (four patients) and tonic-clonic seizurelike activity (two patients). Doses ranged from 1/4 teaspoon to 4 tablespoons. Acute symptoms resolved within 7 hours. GHB was investigated as an anesthetic agent during the 1960s until seizures and lack of analgesia precluded its use. It was recently introduced in the health-food market as a food supplement for body builders with claims of anabolic effects by stimulating growth hormone release. GHB remains under investigational new drug status with the Food and Drug Administration and is illegal for over the counter sale. The Food and Drug Branch of the California Department of Health Services has prohibited further sale of this product in California as have health departments in Florida and South Carolina; however, new cases continue to be reported. Health professionals should be aware of the potential health hazards of GHB.