California has become the first state in the nation to set a drinking-water standard for perchlorate, a component of solid rocket fuel. This action eventually could lead to expensive groundwater cleanups in the state. The California Environmental Protection Agency on March 11 set a public health goal of 6 ppb as the level of perchlorate in drinking water that does not pose a significant risk to human health. This public health goal is not a binding standard, but it provides guidance to health authorities who will set regulatory standards for perchlorate in California drinking water. The chemical is known to inhibit the functioning of the thyroid. Contaminated groundwater at military and aerospace facilities threatens some drinking-water supplies in Southern California (C&EN, Aug. 18, 2003, page 37). On the national level, EPA is squared off against the Pentagon, NASA, and the Department of Energy over a health-protective standard for the chemical. The National Academy of Sciences is working on a report, due later this year, on perchlorate in drinking water.