Lithium is an important psychopharmacological agent for the treatment of unipolar as well as bipolar affective disorders. Lithium has a number of side effects such as hypothyroidism and aggravation of psoriasis. On the other hand, lithium has pro-inflammatory effects, which appear beneficial in some disorders associated with immunological deficits, such as human immunodeficiency virus (HIV) infection and systemic lupus erythematosus (SLE). Therefore, immunological characteristics of lithium may be an important consideration in individualized therapeutic decisions. We measured the levels of the cytokines interleukin (IL)-1ß, IL-2, IL-4, IL-6, IL-22, IL-17 and tumour necrosis factor (TNF)-α in the stimulated blood of thirty healthy subjects supplemented with lithium alone, the antidepressants citalopram, escitalopram or mirtazapine alone, the combination of each antidepressant with lithium, and a no drug control. These drugs were tested under three blood stimulant conditions: murine anti-human CD3 monoclonal antibody OKT3 and the 5C3 monoclonal antibody (OKT3/5C3), phytohemagglutinin (PHA), and unstimulated blood. Lithium, alone and in combination with any of the tested antidepressants, led to a consistent increase of IL-1ß, IL-6 and TNF-α levels in the unstimulated as well as the stimulated blood. In the OKT3/5C3- and PHA-stimulated blood, IL-17 production was significantly enhanced by lithium. Lithium additionally increased IL-2 concentrations significantly in PHA-stimulated blood. The data support the view that lithium has pro-inflammatory properties. These immunological characteristics may contribute to side effects of lithium, but may also explain its beneficial effects in patients suffering from HIV infection or SLE.