The implicit-association test (IAT) is a method for measuring subconscious associations between concepts in memory. It is widely used in social psychology research for assessing associations that people may be unable or unwilling to articulate, including those relating to race, gender, self harm, and risk-taking behaviour. We describe the motivation for adapting the IAT to user interface evaluation, including its potential to support rapid A/B testing that is amenable to online crowd-source dissemination, while also potentially reducing the validity risks caused by biases such as the good subject effect. We present a method (the UI-IAT) for conducting implicit association tests for A/B user interface evaluation, and we present results of two experiments demonstrating that, although the method can successfully discriminate between 'good' and 'bad' interfaces, its sensitivity is low. We discuss implications for practical use of the UI-IAT and for further work.