Canada has rejected an application for the approval of the growth hormone bovine somatotropin (BST).
The move has whipped up fresh controversy in the USA, where a food safety organisation has demanded the government review use of the controversial milk production booster.
The Canadian authorities cited risks to animal health as the reason behind the refusal to grant a licence, and not the suspected dangers to human welfare. The US Centre for Food Safety responded by calling on the Food & Drug Administration (FDA) to take another look at the licence it granted BST in 1993.
In reply, US Secretary of Health and Human Services Donna Shalala said: