The effects of electroconvulsive therapy (ECT) on serum levels of the acute-phase reactant C-reactive protein (CRP) and intracellular enzymes such as alkaline phosphatase (ALP), lactate dehydrogenase (LDH), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and creatine kinase (CK), have received little attention. If brain cells are damaged, CK-BB, LDH and AST levels are expected to show (minor) elevations. We measured serum levels of prolactin, AST, ALT, LDH, ALP, CK and CRP before and 5 min, 30 min, 4 h, 1 day, 2 days, and 3 days after ECT in 15 consecutive patients (eight women and seven men; mean 53.9 years old, range 3082) who did not receive ECT in the preceding 2 weeks. Prolactin levels increased (P = 0.001), but none of the other mean concentrations significantly increased over time. All concentrations remained within the normal range in every patient, except for five samples with elevated CK levels (range 333-675 IU/l). CK-MB and CK-BB fractions, however, remained low, indicating that skeletal muscle was the source of the CK elevation. Serum levels of markers of brain cell leakage and inflammation remained low following one ECT session, suggesting that ECT does not cause direct brain cell leakage, nor an inflammatory response.