Induced systemic resistances (ISR) is defined as the enhanced resistance exhibited by a plant, appropriately stimulated, upon 'challenge' inoculation with a pathogen. Hypersensitive reaction was first related to ISR, then it was observed that challenge inoculation of distant tissues resulted in smaller and fewer lesions (systemic acquired resistance, SAR) than in non-induced plants. This response is related to several biochemical changes in the plants. In a greenhouse trial, tobacco seedling roots were inoculated with an isolate of Gliocladium roseum (GNL) well-known as an antagonist of many crop plants, followed by a challenge inoculation with a pathogenic strain of Erysiphe orontii on leaves. Two weeks later, vegetative growth was recorded before the plants were dissected in leaves, stalk and root. Lyophilized leaves were extracted with appropriate buffer and extracts were analyzed for ß-1,3-glucanases, ß-1,4-glycosidases, N-acetyl-ß-D-glucosaminidase and ß-D-N-N¹-diacetyl-chitobiosidase activities. Methods used were: quantification of reducing sugar using laminarine as substrate for glucanase, spectrophotometric evaluation of the release of p-nitrophenol from p-nitrophenil-ß-D-glucopyranoside, p-nitrophenyl-N-acetyl-ß-D-glucosaminide and p-nitrophenyl-ß-D-N-N¹-diacetychitobiose for the last three enzymatic activities, respectively. Furthermore, peroxidase isozymes pattern was determined with polyacrilamide gel electrophoresis (PAGE).Leaves of plants inoculated with GNL, in comparison with the uninoculated control showed: 1) an increased activity of ß-1,3-glucanases, ß-1,4-glycosidases and N-acetyl- ß-D-glucosaminidase; 2) a new band and a major intensity for other two bands in peroxidase isozymes pattern; 3) no increase of a low level of chitobiosidase activity; 4) fewer number and spare colonies on leaves similarly inoculated with E. orontii and GNL isolate. This is the first time that this behaviour is demonstrated for a Gliocladium roseum isolate.