Seasonal variations in mood and behaviour appear to be best understood through an integration of biological and psychological research. Disturbances in mood are the main psychological component of seasonality. This paper examines the hypothesis that elevated levels of mood variability, decreased average levels of positive affect and increased average levels of negative affect may be characteristic of the overall mood profile associated with acute seasonal disturbances in mood and behaviour. During the winter months of January and February, 59 volunteers (10 males, 49 females; overall mean age=28) completed the Seasonal Pattern Assessment Questionnaire (SPAQ) and subsequently completed the 20-item version of the Positive and Negative Affect Schedule (PANAS) twice daily for a fortnight. Participants were not clinically diagnosed sufferers of Seasonal Affective Disorder (SAD). Mood profile co-varied with severity of seasonal disturbances in mood and behaviour. While seasonality was unrelated to average mood levels, it was significantly positively associated with mood variability. Considering SAD as the extreme end of the continuum of intensities of seasonality, further examination of the biological and psychological importance of mood variability within the aetiology of SAD is warranted. (C) 2003 Elsevier Ltd. All rights reserved.