Derivative thermogravimetric (DTG) analysis was carried out on a set of dried perennial ryegrass (Lolium perenni) samples with known dry matter digestibility in the 60, 70 and 80% ranges as determined by acid pepsin and cellulase assays. This analysis was undertaken to determine relationships between DTG weight loss parameters and dry matter digestibility (DMD). The effects of three (5, 20 and 500 degreesC/min) heating rates under dynamic and isothermal runs were investigated to identify optimum experimental conditions. The weight loss in a minor peak associated with the primary peak, under both dynamic and isothermal conditions was reduced with increasing digestibility of the grass samples and additional effects on both the primary and secondary combustion peaks were also observed. The results of this study suggested that DMD values for grasses could be determined from the thermograms. The advantages of using different heating rates with associated effects on the thermal profile of the different fibre fractions are discussed.