A flow cell incorporating a stationary carbon paste electrode coupled with a.c. voltammetry was used. Preconcentration and determination of the cancer chemotherapy drug mitoxantrone (MXT) were achieved via a flow-injection approach utilizing adsorption of the drug on the electrode, followed by medium exchange and a.c. voltammetry on the adsorbed surface. A linear response was obtained in the concentration range 5 × 10 −9–1.5 × 10 −7 M with aqueous samples. The method was used for the determination of MXT in urine without any sample pretreatment; the relative standard deviation obtained was 1.1% ( n = 5) with a concentration of 1 × 10 −6 M. The proposed method is more selective than other methods suggested for the determination of MXT in urine and plasma samples, which usually require some kind of sample pretreatment.