A specific method for the spectrophotometric determination of total steroidal sapogenin, based on colour reactions with anisaldehyde, sulphuric acid and ethyl acetate and applicable to microgram amounts, is described. It has been shown that this determination can be carried out directly on a saponin solution and that there is virtually no interference from sugars, sterols, fatty acids and vegetable oil. The sapogenins have the same colorimetric properties whether they are in the free state, bound with sugars, esterified with acetic acid or mono- or polyhydroxylated. The method described is accurate (relative error 1.4%), rapid, easily automated and gives a chromophore with the same absorption spectrum with only one peak at 430 nm for all of the sapogenins tested: diosgenin, tigogenin, hecogenin, smilagenin, yonogenin, tokorogenin, etc. The molar absorption coefficient is approximately 49 000.