A TEST of ‘steadiness’ has been used in this Department as a class experiment, in order to illustrate the importance of the ‘double blind’ principle in the design of controlled clinical trials. The apparatus of Seashore and Adams1 was chosen. Steadiness is measured as the ability to hold a metal stylus in position for a fixed period within holes of graduated diameters, drilled in a metal plate, without allowing the stylus to come into contact with the sides of the hole. An index of steadiness is obtained by multiplying the contact times for each hole by arbitrary factors related to the hole diameters, and summing the result.