Two techniques for determining endothelial viability have been reported, ie, tissue culture and para-nitroblue tetrazolium (PNBT) staining. A comparison of these methods was undertaken to determine whether they gave comparable results. Rabbit corneas were stored in refrigerated serum for one to five weeks. The corneas were then bisected, one half stained and the endothelium of the second half cultured. As a series, the results from the two methods were much the same, but in some individual cases there was a wide variance between the two estimates. In general it would appear that either method, in a large series, gives a fairly true estimation of the endothelial viability, but both methods in isolated cases may give inaccurate results.