The functional neuroanatomy of verbal working memory is a potential diagnostic biomarker for depression. Twenty patients with unipolar depression and 20 healthy controls performed a variable load version (n-back) of the task. Functional MRI data were analysed with support vector machine methods. Diagnostic classification was highest at the mid-level of task difficulty (2-back) (sensitivity 65%, specificity 70%, P<0.009). Significant classification of clinical response (>or=50% reduction in clinical symptom ratings) was found at the most difficult level (3-back) (sensitivity 85%, specificity 52%, P<0.003). The functional neuroanatomy of verbal working memory provides a statistically significant but clinically moderate contribution as a diagnostic biomarker for depression, whereas its potential as a neural predictor of clinical response requires further investigation.