Pontoporeia affinis was maintained in the laboratory at 6 C for over 3 months, during which time the animals reproduced successfully. They appeared to require a silty substrate into which they could burrow, and any marked circulation or agitation of the water had an adverse effect upon them. A mixture of a powdered egg‐yolk preparation and dehydrated cereal‐grass leaf powder was the most successful food source. Temperature tolerance tests resulted in a 24‐hr TLm of 12 C, a 96‐hr TLm of 10.8 C, and a 30‐day TLm of 10.4 C.