The aim of the present study was to examine the oxidative properties and an assay of azithromycin and Hemomycin (R) at a gold electrode in neutral electrolyte using cyclic linear sweep voltammetry. The maximum value of the current of the oxidation peak of pure azithromycin and azithromycin from Hemomycin (R) at 0.6 V versus SCE in 0.05 M NaHCO3 and in a mixture methanol -0.05 M NaHCO3 (1:1) at a scan rate of 50 mV s(-1) is a linear function of the concentration in the range of 0.235-0.588 mg/cm(3). HPLC analysis of the bulk of electrolyte confirmed the data obtained by analysis of the values of the current peak concerning the concentration of antibiotic in the investigated concentration range. The role of methanol, when present, is discussed. In the case of azithromycin, the presence of methanol leads to higher current peak values. However, in the case of Hemonlycin (R), methanol should be avoided because of its inhibiting influence on the qualitative and quantitative determination of azithromycin and on the azithromycin/lactose, separation. (c) 2005 Elsevier Ltd. All rights reserved.