In this work, direct and indirect methods for determination of vitamin K 3 were developed using differential pulse polarography. The reaction between sulfite and the quinone (Q) form of vitamin K 3 was used for indirect determination, since the sulfite peak at -0.7 V is sharp and very reproducible in 0.1 M HAc NaAc (pH = 5.5). It was found that at pH 4.5-5.5, this reaction was quantitative and very fast when the temperature was 45 • C. For its direct determination, on the other hand, vitamin K 3 was standardized by the indirect method using standard sulfite as the reducing agent. The calibration graph for vitamin K 3 (in Q form), using the peak at -1.0 V in a HAc-NaAc medium with a pH of 5.5, was linear for concentrations ranging from 5 × 10 −7 to 3 × 10 −5 M, and the limit of detection (LOD) was 1.5 × 10 −7 M. The proposed methods were successfully applied to the determination of vitamin K 3 in a clinical injection solution and in blood serum.