1.   Scientists are divided on the question of whether trace levels of nerve gas and other chemical weapons could produce the health problems found among the veterans.

2.   Baffert and his attorney, Neil Papiano, contend there were trace levels of morphine in the filly through accidental contamination of her feed.

3.   The maximum acceptable trace levels for five types of anabolic steroids, which are used to build muscle mass, have been sharply reduced.

4.   Trace levels of sulfur dioxide emissions lead to acid rain, environmentalists say.