A method for preserving field collected material in frozen condition for electrophoresis is described. A mixture of ice and salt was used to obtain a freezing temperature of -20 degrees C. Field collected mosquitoes can be stored for up to 9 or more days in an ordinary thermos bottle by replacing the ice-salt mixture at 3-day intervals, without loss of enzyme activity. This method is a considerable improvement for the shipment of material from the field to the laboratory.