Cyproheptadine hydrochloride (C) shows an antihistaminic as well as antimuscarine, antiserotonic and sedative activity. The present work describes sensitive and reasonably selective poly(vinyl chloride) membrane electrodes for cyproheptadine. They are based on the use of cyproheptadine-tetrakis(4-chlorophenyl)borate (C-TClPB) and cyproheptadine-dipicrylamine (C-DPA) as a novel electroactive compound. Cyproheptadine ion-selective poly(vinyl chloride) membrane electrodes contain an ion-pair complex of cyproheptadine with 2-nitrophenyloctyl ether (ENPO), 2-nitrodiphenyl ether (ENdP), bis(2-ethylhexyl)sebacate (DOS) and 1-isopropyl-4-nitrobenzene (IPNB) as solvent mediators. The performance of the electrodes was investigated by measuring the e.m.f. values of 10(-2)-10(-7) mol l(-1) cyproheptadine hydrochloride. The effect of pH on the potential readings of the cyproheptadine electrodes was checked by the recording on the e.m.f. of 10(-3) mol l(-1) cyproheptadine hydrochloride with pH values from 2.5 to 7.0. Potentiometric selectivity coefficient were measured by the separate solution method using a 10(-3) mol l(-1) concentration of cyproheptadine and the some concentration of interferent cations. The electrode obtained with C-TClPB with DOS and electrode with C-DPA with IpNB were used in the potentiometric determination of cyproheptadine in bulk substance and tablets PERITOL 4 mg as indicator electrodes. The results are in good agreement with those obtained by UV spectrophotometric method.