The following glycosides of 4-trifluoromethylumbelliferone: alpha-D-mannopyranoside, alpha-L-fucopyranoside, alpha-D-glucopyranoside, beta-D-glucopyranoside, alpha-D-galactopyranoside, beta-D-galactopyranoside, alpha-L-iduronide and beta-D-glucuronide were studied. 4-Trifluoromethylumbelliferyl glycosides were shown to be substrates for glycosidases. Some of them were cleaved even better than the corresponding methylumbelliferyl glycosides. 4-Trifluoromethylumbelliferyl glycosides were applied for revealing the corresponding enzyme deficiencies upon diagnosis of Gaucher and Hurler diseases as well as GM1 gangliosidosis and alpha-mannosidosis. 4-Trifluoromethylumbelliferone released after enzymatic hydrolysis of 4-trifluoromethylumbelliferyl glycosides exhibits more contrast yellow fluorescence in UV-light than the blue one of methylumbelliferone upon exposure of enzyme activity on solid supports. Therefore 4-trifluoromethylumbelliferyl glycosides are convenient substrates for revealing glycosidase activity directly in tissue samples, e.g. in placenta, and thus for fast prenatal diagnosis of lysosomal diseases.