The cryopreservation of standard sera

To determine the storage temperature needed for the preservation of standard sera for serodiagnostic tests, groups of sera were tested before and after storage at - 70°C and - 20°C for periods of up to five years. The temperature required depended on the nature of the test, but no definite advantage was found in storage at -70°C. For complement fixation this temperature was inadequate and greatly inferior to liquid nitrogen. For immunofluorescence it had no apparent advantage over a temperature of -20°C, and for some other tests it was no more than marginally superior.