A microdi †usion method with solid-phase detection for the determination of total cyanogens (\cyanogenic potential, CNp) in fresh cassava roots was developed and evaluated against the classical spectrophotometric method of Cooke (J Sci Food Agric 29 (1978) 345È352). Using seven di †erent cassava cultivars, a signiÐcant di †erence (approx 15%) in the determined CNp was observed only for one of these. The new method o †ers several advantages over the earlier described spectrophotometric methods. Filtration of homogenates is not necessary, neither is cooling nor heating. The developed colour is stable on the reaction sheet, so that levels may be measured immediately or when appropriate, and be Ðled for documentation purposes. Further the solid-phase reaction may be measured in di †erent ways according to the instrumentation available, ie reÑectometry as used in this study, or absorption of transmitted light using a TLCdensitometer or a microplate reader. The amount of enzyme (linamarase) used per analysis is lower than for the spectrophotometric assays, giving economic advantages to the present assay. In addition to the extract, only three solutions are used when performing the assay, ie the bu †er, the substrate solution for standards, and the enzyme solution. The assay may be run either according to a "slowÏ overnight protocol or to a "fastÏ protocol at 40¡C. 1998 SCI.