The differential effects of two forms of feedback on energy consumption behaviour were examined in two units of a metallurgical company. In one unit, employees received information about energy conservation, had to set goals and received feedback on their own conservation behaviour. The same procedure was followed with employees in a second unit, but they also received information about the performance of the first unit. In accordance with predictions from social identity theory and social comparison theory, the results clearly showed that employees in the comparative feedback condition saved more energy than employees who only received information about their own performance, even half a year after the intervention. A remarkable finding was that behavioural change took place with hardly any changes in attitudes or intentions. The discussion focuses on these findings and on their implications for organizational behaviour change in general.