The evaluation of seed physiological quality can help taking quick decision about the use or disposal of lots for conservation. The tetrazolium test is one of the most traditional in the analysis of seeds quality. Optional preconditioning procedures have improved the efficiency of this test. This work compared the efficiency of different preconditioning procedures, the buffered solution, concentrations and exposure time to tetrazolium solution in assessing the quality of orchid seeds of Cattleya labiata and Cattleya tigrina lots. The analysis was made through magnification of digital images. For preconditioning evaluation, two seed lots were aliquoted and submitted to different treatments: 10% sucrose solution, 10% glucose solution and water at room temperature for 24 hours. After preconditioning, seeds were immersed in tetrazolium solutions -prepared with buffer or water -at concentrations of 0.1, 0.5 and 1.0% for periods of 3, 12 and 24 hours, at 40 °C, in a water bath, in the dark. The experiment design was arranged in a factorial 4x3x3x2 and the mean comparison was made by Tukey test at 5% probability. Tetrazolium test in preconditioned orchid seeds allowed better visualization of red viable seeds. Tetrazolium test in orchid seeds preconditioned in glucose 10% solution or sucrose 10% solution was more effective for viable seeds visualization. Diluting tetrazolium salt in buffered solution or water made no difference for the results. Maintaining seeds in contact with tetrazolium 1% solution for 24 hours provided the higher viability values for both seed lots.