The objective of this research was to develop an appropriate tetrazolium methodology for viability and vigor evaluation of squash seeds. The following procedures were tested for pre-conditioning of the seeds: moistening in wet paper towel for 16 to 24h at 25°C; immersion in water for 15, 30 and 60 minutes at 40°C for tegument removal, and for 30 and 60 minutes for removal of the embryo surrounding internal membrane. The embryos were then immersed for 30, 60 and 90 minutes in 0.05 and 0.075% tetrazolium solution, at 40°C, for coloration. Each sample submitted to the tetrazolium test was also evaluated by the germination and seedling vigor tests and five viability and vigor classes were established . This procedure was applied to eight seed lots and the results were validated by the germination, accelerated aging and seedling emergence tests. The tetrazolium test was efficient in evaluating squash seed viability and vigor. The ideal procedure was seed immersion in water for 30 minutes at 40°C, for removal of the tegument followed by a further 30 minutes in water for the internal membrane removal. The ideal coloration was obtained after 60 minutes immersion in a 0.05 or 0.075% tetrazolium solution at 40°C.