Summary: Six hundred forty-five chickens and ten rabbits were used for precipitin-production. Chickens were found to be excellent precipitin-producers when injected with quantities as low as 1.75 ml of a 1:9 dilution of serum-protein. The titer of chicken-antisera changes upon standing. Tests made after nine or more days showed a marked increase over the titers secured within 24 hours after bleeding. Rabbit-antisera did not show such changes. Titers of 1:8,096,000 were frequently secured after three series of injections, and one antiserum gave a titer of 1:32,384,000.