Extending an invitation can do more than bring in a guest — it can build a beneficial relationship. In 2005, the Feinstein Institute for Medical Research in New York named cytokine specialist Jan Andersson, head of infectious diseases at the Karolinska Institute of Stockholm, as its first invited lecturer. Andersson reciprocated by suggesting that the two institutes combine educational forces.

This month, they announced a joint training programme that will let Karolinska graduates do postdoctoral research in New York while Feinstein scientists have access to Karolinska labs. Both institutions have records of collaboration and mentorship that will be strengthened by the relationship, says Feinstein director Kevin Tracey. He and Andersson, for example, have worked together on the role of cytokines in inflammation.

The Feinstein Institute's research enterprise, with 750 employees doing research in 45 programmes, is about a third the size of the Karolinska's and lacks some of its infrastructure, such as mass spectrometry and proteomics facilities. However, it has strengths in inflammation research, neuroscience and neuropsychology that the Karolinska wants to tap into. “The Karolinska is much larger and has more departments, people and programmes,” Tracey says.

Meanwhile, the Karolinska wants to augment its translational and clinical research. The Feinstein can help, as it is affiliated with the North Shore–Long Island Jewish Health System, which boasts 38,000 patients in 15 hospitals; 120,000 patients have been enrolled in clinical trials since 1998. The Feinstein serves the greater New York area, with 8 million people, close to Sweden's total population.

The Karolinska's medical and graduate training is strong, says Tracey, “but they were interested in having help with their postdoctoral training.

Both institutions offer high-quality mentoring. The Karolinska Institute launched its junior faculty programme in 2004, helping graduates make the transition to independent researcher (see Nature 427, 470; 2004). The Feinstein Institute specializes in making doctors who have practised medicine into researchers. And most do continue in research, unlike graduates from many other such programmes.

Each institution will host up to six researchers. Those interested in working in the other institute's lab must apply for a place and be reviewed by a joint admission committee, including scientists from both institutes.