United Nations Secretary-General Kofi Annan has called on trading nations to do more to help the poor benefit from international commerce.
Opening the UN Conference on Trade and Development in Sao Paulo, Mr Annan urged participants to create a "development based approach to trade".
"Let us help developing countries take full advantage of trading opportunities," he said.
The talks are seen as a chance for poor nations to get a better deal.
The conference itself does not make trade rules, which is the job of the Word Trade Organisation.
Talks broke down in 2003 at the last WTO meeting in Cancun, Mexico, after developing countries insisted that the West agree to reduce agricultural subsidies.
Critics claim these subsidies allow farmers in the developed world to export their goods onto the world market at an artificially low price, making it difficult for farmers in poorer countries to compete.
At the same time, industrialised nations are accused of protecting their domestic markets for agricultural products through import duties.
Speakers in Sao Paulo are expected to urge developing countries to forge a single negotiating position in future trade talks with their rich counterparts.
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Brazilian president Luiz Inacio Lula da Silva, who has spearheaded efforts to unite the developed world in trade talks, said trade relations should be reformulated so as to give poor countries access to technology and investments.
"Globalisation is not synonymous with development, it is not a substitute for development, but it can be used as an instrument for development," he told delegates.
Divide and rule
And Thailand's prime minister Thaksin Shinawatra suggested that developing countries may focus on trading with each other rather than with the west if rich countries fail to open their markets.
"My solution is that we try to reduce our dependence on developed country markets," he said.
Speaking on Sunday at one of the many preliminary events, Mr Annan stressed the need for changes in trade.
The sad truth is, he said, that the world is a more unequal place than it was 40 years ago when the UN Trade and Development Conference was founded.
Getting world trade talks moving again is being seen as a matter of urgency at the conference.
Many developing countries fear that if no progress is made this year, it will allow the rich nations to divide and rule.
They predict Europe and the United States will make a series of separate trade agreements to gain access to the markets of developing countries without having to make serious concessions themselves.