The polarographic behaviour of 7-[D(–)-α-(4-ethyl-2,3-dioxo-1-piperazinecarboxamido)-α-(4-hydroxyphenyl)acetamido]-3-[(1-methyl-1H-tetrazol-5-yl)thiomethyl]-3-cephem-4-carboxylic acid was studied. The sample yields a clear single-sweep oscillopolarographic wave at about –1.1 V in KH₂PO₄-Na₂HPO₄ buffer solution. The relationship between peak current and concentration is linear in two different concentration ranges. The results prove that the wave has adsorption characteristics. A mechanism is proposed for the reduction of the sample.