Bispyribac-sodium was well degradable in both soils under aerobic conditions. In the course of the experiment, several 14C-regions were detected and quantified together with unaltered bispyribac-sodium and material remaining at the origin of the TLC separation. However, only two major degradation products occurred, i.e. amounted to > 10% of the applied radioactivity at any time during the study. The first metabolite was identified as DesMe-2023 (M06), with a maximum of 12.8% and 14.4% of the applied radioactivity on day 3 in Isola della Scala soil (pyrimidine-label and phenyl-label, respectively). The corresponding maximum values for the Nogarole Rocca soil were below 10% (7.9 and 8.7% at day 7) of the applied radioactivity. The second major metabolite was Na-BX-180 (M05), with maximum values of 5.9% (pyrimidine-label) and 15.0% (phenyl-label) on day 15 in Isola della Scala soil. The corresponding maximum values for the Nogarole Rocca soil were 7.5% (pyrimidine-label, day 57) and 14.7% (phenyl-label, day 119). A minor degradation product, identified as Na-DesMe-180 (M10), occurred mainly in Isola della Scala soil, in which the maximum was 1.4% (pyrimidine-label, day 15) and 3.3% (phenyl-label, day 57). Another minor degradation product, identified as an isomer of Na-DesMe-180 (M10), was found several times above the limit of quantitation (LOQ) in the test series of Nogarole Rocca soil, especially towards the later sampling dates. For this compound, the maximum was 4.8% (pyrimidine-label) and 5.5% (phenyl-label) of the applied radioactivity both on day 91, decreasing to 3.6% and 4.2% on day 119. All the other individual 14C-regions detected (including “origin”), corresponded to < 3.6% and < 2.0% of the applied radioactivity for the soils Isola della Scala and Nogarole Rocca, respectively. They showed no trend towards an increase at the end of the test. Two of these trace metabolites were characterised as Me2BA (M03) and MeBA (M04). Comparing the analytical results received from the test series with the different radiolabels, it was shown that there is no relevant difference in product formation in the soil extracts. The predominant portion of degradation products contained both, the phenyl ring as well as at least one of the two pyrimidine rings. After the initial desmethylation step of one of the pyrimidinyl moieties of bispyribac-sodium, leading to DesMe-2023 (M06), the molecule was further degraded to Na-BX-180 (M05), and finally to CO2. Na-BX-180 (M05) may have been formed directly from the parent compound as well. The study demonstrated that bispyribac-sodium was well degraded in aerobic soil. The major metabolites formed are further degraded and, therefore, do not accumulate in soil.