Specular microscopy shows the integrity of the endothelial cell pattern, and vital staining methods allow the evaluation of endothelial viability. Dyes commonly used such as trypan blue enter the cells passively through the disturbed membrane. The uptake of fluorescein diacetate (FDA) is an active process. To compare the efficiency of the two methods we performed double stainings and examined the results. Pig cornea endothelium was stained by both trypan blue and FDA and vital and non-vital cells were compared. More non-vital cells were stained by FDA than by trypan blue, indicating that cells with membranes that are not permeable by trypan blue cannot metabolize FDA. This fact is important where estimating the endothelial viability of donor corneas.