Recombinant bovine somatotropin, or rBST, is an artificially produced hormone that is injected into cows to increase their milk production, typically by 10 percent to 20 percent.

The hormone was controversial even before it was approved by the Food and Drug Administration and went on the market in early 1994. It is banned in Canada and Europe.

Posilac, manufactured by Monsanto Co. of St. Louis, is the only growth hormone approved by the FDA for use on dairy cows.

According to the U.S. Department of Agriculture, 22 percent of all dairy cows in the United States were given rBST last year, up from 10 percent in 1996.

Monsanto won’t divulge its sales of Posilac, but has said in court documents that total Posilac sales since 1994 exceed $1 billion. Monsanto’s 2002 annual report says Posilac sales increased 6 percent last year.