Authorities in the United States have given preliminary approval to a plan to grow rice genetically modified to produce human proteins.
Rice plants including human genes involved in producing breast milk would be grown in the state of Kansas.
The company behind the proposal, Ventria Bioscience, says the plants could be developed into medicines for diarrhoea and dehydration in infants.
Critics say parts of the rice plants could enter the food chain.
Under the proposal, which received preliminary backing from the US Department of Agriculture last week, Ventria would plant rice over some 3,000 acres (1,215 ha) of farmland in the mid-western state.
The company said it would take precautions to ensure the seeds did not mix with other crops.
'Dealing with an unknown'
But critics say that bad weather such as high winds or human error could lead to problems.
"I'm really concerned about this, because I think firstly there is this potential for this rice to get into the food supply, and secondly, it hasn't been tested," said Bill Freese of the US Center for Food Safety.
"It hasn't gone through a drug review process. So we're dealing with an unknown here - something that could cause harm to human health."
With controversy growing, the US Department of Agriculture has yet to give final approval, says the BBC's James Westhead in Washington.
And even then, our correspondent adds, there are huge regulatory hurdles before food containing human DNA could actually be sold to consumers.
The public has until the end of March to submit objections to the plan, the Associated Press news agency reported. If final permission is given, Ventria will begin planting rice in April or May, company president Scott Deeter said.