A novel electrocatalytic material for oxygen reduction, based on polyaniline in combinationwith copper, was developed and utilised for the direct voltammetric quantification of ammonium ions. Consecutive electrode modification by electrodeposited copper, a Nafion membrane and electropolymerised polyaniline resulted in an electrocatalytic composite material which the retained conductivity at neutral pH. Ammonia complex formation with Cu (I) caused the appearance of oxygen electrocatalysis, which was observed as an increase in cathodic current. This Faradaic phenomenon offered the advantage of direct voltammetric detection and was utilised for ammonium electroanalysis. The developed quantification protocol was applied for ammonium assay in human serum and compared with the routine approach for clinical analysis.