For the first time supercomputers in the UK and the US have been linked to carry out an interactive scientific experiment. It involves three of the most powerful computing resources in the world working in parallel with each other. This is the first demonstration of the use of the "Grid" to simultaneously link the high performance computers with remote visualisation centres in the UK and the US. This allowed scientists to interact with the computer models as they evolved in real time. The "TeraGyroid" experiment was jointly funded by the UK's Engineering and Physical Sciences Research Council (EPSRC) and the National Science Foundation, USA (NSF). TeraGyroid is based on the e-Science pilot project RealityGrid. The UK part of "TeraGyroid" involved the CSAR and HPCx high performance computer facilities, both administered by EPSRC, on behalf of Research Councils UK. In the US the resources on NSF's Extensible Terascale Facility (ETF) were used. The link between these computing facilities was provided by the UK's e-Science Grid (administered by EPSRC on behalf of Research Councils UK) and the USA's TeraGrid. The e-Science "Grid" is intended as the natural successor to the Web – moving beyond the provision of seamless access to information to providing seamless integration of computer, data and other remote sources. The experiment was coordinated from the Supercomputing 2003 conference in Phoenix, Arizona, USA from 00:00 Tuesday 18th November to 24:00 Thursday 20th November (GMT). The experiment involved all of the high performance computing resources carrying out lattice Boltzmann calculations. This has never been done before on this scale and in such a limited space of time (72 hours). Lattice Boltzmann methods are complex theoretical calculations to model complex self-assembly and fluid flow. The success of this experiment demonstrates that this linking of multiple high performance computers can allow scientists to expand their knowledge of small systems containing a few molecules to larger, macroscopic, real-world situations containing hundreds of thousands of billions of molecules. EPSRC's Director of Research and Innovation, Randal Richards, said: "This illustrates the increasing role that supercomputing power is taking in science, engineering and technology research. It also demonstrates, in line with a recent statement from Research Councils UK, that investment in such high end computing is strategic to the science and engineering base of the UK."