Preservation of two protozoan parasites, one intracellular Pla smodium berghei, and another extracellular Toxoplasma gonodii was attemptea utilizing the available facilities of mechanical freezing at-20 &-70°C. Viable preservation was accomplished by rapid and slow freezing, using glycerol and dimethyl sulphoxide as pro tectants in various concentrations. It might be safely concluded that rapid freezing is the method of choice for viable preservation of these tow organisms. Glycerol seems to afford better protection than dimenthly sulphoxide for intracellular parasites. Furthermore the period of preservation is positively correlated with the concen tration of glycerol. As diluents for the protectants, phosphate buffer saline and calf serum are likely less efficient than rat serum. Washing of the infective material was intended to abolish the possible harmful effect of coexisting antibodies. However, this step did not seem to enhance the period of preservation.