A new method was established for the simultaneous determination of Sn(II) and Sn(IV) using differential pulse polarography (DPP). Among several electrolytes, 0.1 M NaOH in the presence of 0.1 M KNO3 was found to be the most suitable one. In this medium, Sn(II) had 2 peaks, at -0.74 and -1.17 V, which were sharp and very sensitive. Sn(IV), on the other hand, had a very small peak at -0.92 V when its concentration was higher than 4.0 x 10(-4) M. Thus, it was decided to determine Sn(IV) after reduction into Sn(II). In the presence of both Sn(II) and Sn(IV), Sn(II) was first determined from the peak at -1.17 V, and then Sn(IV) was determined after its reduction with NaBH4 into Sn(II). The detection limit was 5.5 x 10(-7) M and 8.2 x 10(-7) M for Sn(II) and Sn(IV), respectively. The interference effect of the most common ions, Fe(III), Cu(II), Pb(II), Cd(II), and Zn(II), was investigated. Only copper and iron had an interfering effect during the speciation procedures, since they oxidized Sn(II), which was formed after reduction of Sn(IV) for its determination. This effect of Cu(II) and Fe(III) ions could be eliminated by the reducing agent NaBH4, which was used for the reduction of Sn(IV). Since Pb(II) and Cd(II) peaks overlap with the first peak of Sn(II) at -0.74V, Sn(II) was determined using the second peak, at -1.17 V. In a synthetic sample containing Sn(II), Sn(IV), and all common ions, the total content of tin (2.0 x 10(-5) M) was found to be (2.07 +/- 0.38) x 10(-5) M (90% CI, N = 3).