"We are certainly more optimistic than before to get something substantial in Cancun," a source close to the World Trade Organisation talks said Monday.

Agreement reached Saturday by the 146-member WTO on improving access to generic drugs so poor countries can better fight diseases like AIDS, malaria and tuberculosis cleared the way to the Cancun meeting on September 10-14.

"If it had popped up in Cancun, negotiations would have been in real trouble," the source said.

A European source in Geneva said the weekend accord "is very, very important politically. It's a good sign, before getting started (in Mexico), that the ministers' time will not be wasted on this very technical issue."

The Cancun conference is aimed at giving a boost to the Doha round of global trade talks -- launched in the Qatari capital at the end of 2001 -- and which are supposed to be wrapped up by January 1, 2005.

Those talks target development of the world poorest countries, which seek concrete measures by developed nations before further opening domestic markets.

Given those goals, the issues of generic drugs and agricultural products became top priorities, with developing countries demanding progress before granting concessions on trade in industrial products, services, investments or access to public markets.

With the pharmaceutical accord taken care of, the potentially more difficult issue of agriculture should now take center stage.

"Without an accord on medicines, everything would have been very difficult in Cancun," agreed Luiz Felipe de Seixas Correa, Brazil's ambassador to the WTO.

"But that does not mean that with an accord everything will now be easy."

Success of the Doha round depended on opening developed countries' markets to agricultural products, he added.

"If we don't find a solution to the agricultural question, we won't negotiate on the others."

In mid August, the United States and the European Union agreed on a common position that would reduce subsidies to their respective farmers.