This study examined relationships between working memory and subjective states on four successive occasions. Participants (n=112) performed a task requiring concurrent mental arithmetic and ordered recall of single words under increasing levels of time pressure. Subjective state was measured with the Dundee Stress State Questionnaire (Matthews et al., 2002), before and after performance on each occasion. Findings suggested reciprocal influences of state and working memory. Performance elicited state changes including increased task engagement and distress. However, state-change patterns themselves changed across days of testing, suggesting progressive adaptation to the task environment. State dimensions including lower distress and higher task engagement correlated with working memory. Structural equation modelling suggested a stable influence of states on performance across days. The dynamic interdependence of states and performance is discussed in relation to the transactional model of stress and emotion. © 2009 Psychology Press.