A simple method for freezing cultured human donor material with dimethyl sulfoxide (DMSO) was developed empirically in a commercially available microcomputer-controlled apparatus allowing reproducible freezing curves to be made. The optimum cooling rate was found to be 1.0 °C/min down to –40 °C and then 5.0 °C/min to –80 °C. Total cell loss rates were 36.9 ± (SD) 19.8% of postmortem endothelial cell counts. An improved method for evaluating endothelial viability was applied, which enabled us to observe definite cell survival after a postculture period.