The equipment and techniques for an investigation into the mechanisms which deposit sub-micron particles on to turbine blades are described, with particular reference to the deposition of fog within the low-pressure steam turbine. The experimental studies were centred around a cascade of blades in an open-circuit low-speed wind tunnel. Deposition on the blades of small solid uranine particles entrained in the main air flow was detected and measured using the fluorescent properties of the particles. Some results from preliminary deposition tests are given.