In the last two decades, there has been a considerable increase in pasture areas planted to grasses of the Brachiaria genus, which was followed by a proportional increase in production and utilization of their seeds. This brought about the need of investigations on an adequate evaluation of their germinative power and storability. With this objective, ten lots of Brachiaria brizantha seeds of the cultivar Marandu, from the 92/93 crop year, had their physiological quality evaluated at the beginning and at every two months until twelve months, and at eighteen months of storage in uncontrolled warehouse conditions in the Campinas region, State of São Paulo, Brazil. The following determinations were made: germination (just KNO3 0,2% in the substrate), germination after preheating at 40°C for seven days, and tetrazolium viability. The first two kinds of evaluations were made with and without scarification with concentrated sulphuric acid for fifteen minutes, and the countings were made at 7, 14 and 21 days after seeding. Results showed that preheating caused an increase in germination in the first months of storage, when dormancy was deepest. Acid scarification had very positive effect in breaking seed dormancy during the whole storage period. Tetrazolium viability was the most efficient method to monitor the germinative potential and deterioration of the seeds during storage. In all storage periods there were no substancial differences between viability by tetrazolium and germination after preheating followed by acid scarification.