Objective: Previous research has shown that biological (e.g., genetic, biochemical) accounts of depression--currently in ascendancy--are linked to the general public's pessimism about the syndrome's prognosis. This research examined for the first time whether people with depressive symptoms would associate biological accounts of depression with pessimism about their own prognoses and whether a psychoeducation intervention portraying the biology of depression as malleable could decrease prognostic pessimism among symptomatic individuals. Method: In 3 studies, participants were recruited online and assessed for depression symptoms. Those with significant depressive symptomatology (a Beck Depression Inventory-II score of at least 16) rated their endorsement of biochemical and genetic causal attributions for their symptoms and indicated expected length of symptom duration. An audiovisual intervention emphasizing the malleability of gene effects and neurochemistry was developed, and its effects on symptomatic individuals' prognostic pessimism, feelings of agency, guilt, and general hopelessness were measured. Results: Biochemical and genetic causal attributions for depression were significantly associated with prognostic pessimism among symptomatic individuals. The malleability intervention significantly reduced prognostic pessimism, increased feelings of agency, and decreased general hopelessness. Conclusions: Biochemical and genetic attributions for depression are related to prognostic pessimism among individuals with depressive symptoms, and not just among the general public. However, emphasizing the malleability of gene effects and brain chemistry in depression can foster more optimism about depression-related beliefs. (Contains 2 tables and 4 figures.)