Transmission electron microscopy of a thin-sectioned freeze-substituted suspension of human sperm cryopreserved in conventional straws (0.25ml capacity). The cryoprotectant used was glycerol/egg yolk. Ice was nucleated within the straw at -7°C. The sample was then cooled at 1°C per minute to -100°C and then transferred to liquid nitrogen. When viewed by electron microscopy the freeze concentrated material was electron dense due to the protein components of the egg yolk included in the cryoprotectant. A sperm cell embedded within the freeze concentrated material was partially shrunken or distorted, the mitochondria within the mid-piece appear dense.
