Tainted milk made thousands of Chinese babies ill
Six men have gone on trial in China accused of making and selling the chemical at the centre of the tainted milk scandal.
The tainted milk is blamed for killing at least six children and making 300,000 other people ill.
The men are accused of adding melamine to raw milk to make it appear high in protein.
The company at the centre of the scandal, Sanlu, has already filed for bankruptcy.
State television showed the two men in court in handcuffs, their heads bowed, being questioned by three judges.
Police said Zhang Yujun and Zhang Yanzhang illegally manufactured and sold a "protein powder" composed mainly of melamine and malt dextrin, the official Xinhua News Agency reported.
Police said they had found an illegal workshop run by the two men in Shandong province in eastern China, where the men made 600 tons of the fake protein powder, and was the largest source of melamine in the country.
The trial started on Friday at the Shijiazhuang Intermediate People's Court, in the town where Sanlu is based.
Lawyers have speculated that sentences could start at 10 years.
When the scandal broke in September, a chain of melamine producers and middlemen was found to have been supplying milk dealers with the product.
The dealers added melamine to boost the apparent protein content of milk, which had often been watered down to spread the raw product further.
Major dairy companies bought the milk from such dealers, failing to test the milk for purity and nutritional value.
The result was widespread poisoning of babies, the group most vulnerable to tainted milk as it was their only food source.
The crisis has been an indictment of China's food safety regime
Kidney damage was reported in hundreds of thousands of people and at least six babies were killed.
The government scrambled to fight off allegations that it reacted slowly to the scandal, and promised to bring the culprits to court.
Xinhua reported on Thursday that Sanlu has 1.1 billion yuan ($160m) of net debt.
So far, the courts have been rejecting lawsuits filed by the families seeking compensation.
Fonterra, New Zealand's largest dairy conglomerate that held a 43 percent stake in Sanlu, said this week that Sanlu would be managed by a court-appointed receiver who would sell off the company's assets and repay creditors over the next six months.
Fonterra has written off its $114m investment in Sanlu, the company said.
The scandal tarnished China's food industry far beyond its borders.