A drive to increase scientific exchange between the United States and Cuba is off to a slow start. In the past four months, Cuban officials have cancelled two planned trips of top US scientific leaders to the island nation.

Citing other visitors and events that took up their time, the officials have turned down requests for scientists to enter the country organized by the American Association for the Advancement of Science (AAAS) and the New America Foundation non-governmental organization, both based in Washington DC. In April, the administration of US President Barack Obama said it would work to improve relationships between the two countries, including promoting the "freer flow of information".

The organizers, who have had the trips in the works since before Obama took office, remain hopeful that a delegation might visit Cuba this autumn, says Lawrence Wilkerson, who was chief of staff to former Secretary of State Colin Powell and is working on a New America initiative aimed at Cuba. The delegation is expected to address topics such as tapping Cuba's strengths in biotechnology, pharmaceuticals and studies involving hurricane research, food production and salt-resistant crops.

"Of course we would like more scientific exchange," says Miguel Abad Salazar, a researcher at the BIOECO conservation facility near Santiago in eastern Cuba.

Of course we would like more scientific exchange.

Travel restrictions remain a major stumbling block for US–Cuban collaboration. For instance, US scientists seeking to travel to Cuba can't use federal funds without special government permission. And any US scientist travelling to Cuba must get a licence from the treasury department to spend US dollars there, even if funds come from the private foundations that typically pay for such trips.

It has also been nearly impossible for Cuban scientists to come to the United States; one immediate barrier is the US$150 non-refundable fee for a visa application.

During the Obama administration, however, a handful of Cuban scientists have visited the United States, and US scientists have been increasingly venturing to Cuba. Observers say that the exchanges reflect a growing thaw in bilateral relations, which began before Obama's election.

In May, for instance, David Winkler of Cornell University in Ithaca, New York, went to Cuba to teach an ornithology course to about two dozen scientists at a BIOECO meeting. He went as part of Cornell's Neotropical Conservation Initiative, coordinated by Eduardo Iñigo-Elias, who has been studying in Cuba for years. "The students and scientists were as well trained as anywhere in Latin America," says Winkler. "They would be great ambassadors to work on research projects in other countries." His group hopes to develop such an exchange programme.

These individual exchanges, rather than a coordinated governmental programme, should be the wave of the future, says Peter Feinsinger, a wildlife conservationist who has visited Cuba about a dozen times in the past six years to train biologists. "I favour a scientific grass-roots initiative," says Feinsinger, who works for Northern Arizona University in Flagstaff but is largely funded through the Wildlife Conservation Society in New York. "I think this will happen naturally."

US researchers often partner with colleagues in other countries to do fieldwork in Cuba. For instance, Kam-biu Liu, a geographer at Louisiana State University in Baton Rouge, collaborates with Matthew Peros, an ecologist at the University of Ottawa in Canada, to acquire sediment samples from Cuba to track hurricane history in the region. Peros has to perform the isotopic analysis on the cores for Liu, who cannot use US funds for the research.

None of the US-based funds that flow into the Inter-American Institute for Global Change Research — the organization based outside São Paulo, Brazil, that funds the hurricane work — can similarly be used for work in Cuba. "I have to invent constructs to fund these projects" with funds from other sources, says Holm Tiessen, the institute's director.

Observers hope that more aggressive efforts to ease US–Cuban relations will be forthcoming as more people fill key jobs in the US Department of State.