Immersion fixation of rapidly frozen, untreated tissues and suspensions of cells including spermatozoa.

Small pieces of tissue, and cell suspensions in plastic artificial insemination (AI) 'straws', were frozen rapidly in Freon-12 at -155 degrees C, without pre-treatment. Peripheral fragments were thawed directly in 2% glutaraldehyde at 0 degrees C, and processed for transmission electron microscopy (TEM) studies. Preservation of ultrastructure was satisfactory, and freezing artifacts were minimal.