Prohexadione-calcium degraded rapidly in all soils. Extractable radioactivity declined over the incubation period and there was a concurrent increase in unextractable residues, which generally peaked after 16 to 26 days. Mineralisation in all soils was significant with levels of 14CO2 of 35.3 to 66.5 % AR at the end of the incubation period. Most of the extracted radioactivity was identified as prohexadione. Very small quantities of three metabolites were detected (despropionyl prohexadione, UK1, UK2) and these levels remained < 5 % AR throughout the study.