A t.l.c. method on silicagel plate with a fluorescence indicator has been carried out to increase the native fluorescence of cefotaxime and four of its degradation products. A simultaneous improved fluorimetric quantitation of the compounds in situ is proposed using a chromatogram spectrophotometer. The detectability (0.20 microgram) shows that the procedure is twenty times more sensitive than high-pressure liquid chromatography with u.v. detection; it allows the determination of traces level (1%) degradation products.