1. Results are presented for four years of study on the survival of Artemia cultures when ancestors have been exposed to a series of doses of either radioisotopes or x-rays. Cultures were begun by transferring 10 pairs of adults from a control culture to a 3-liter jar of sea water. Ordinarily, within a generation this gives rise to a culture of several hundred animals. 2. Three-liter cultures did not persist if more than 90 µc. of P32 or more than 30 µc. of Zn65 have been added. Subcultures of 30 µc. of p32 per three liters did not survive a second dose of 30 µc./3L. Also, cultures failed if 2000 r or more of x-rays were delivered to the 10 pairs of adults used to institute the culture. 3. The treatments investigated had no obvious effect upon the original adults. Decline and extinction of the cultures occurred at the first or subsequent generations of offspring. 4. In order to assess reproductive failure, pairs when sexually mature were transferred from the 3-L. cultures to quart jars. All zygotes voided were counted and hatchability was determined for any cysts deposited. Each brood was transferred to a separate container. Progeny surviving to adulthood were counted again and sexed. 5. (a) Decrease both in number of zygotes voided and in survival to adulthood contributed to low adaptive values for experimental organisms. (b) The sex ratio among offspring tends to favor females in control and males in experimental material. 6. Routinely the convenient specific gravity of 1.02 has been used for pair matings and spring reactivation of mass cultures. In 1961 pair mating tests were run in dilute sea water of 1.01 specific gravity and in sea water to which NaCl had been added to reach a specific gravity of 1.07. Both life span and reproductive behavior were improved in brine of 1.07 specific gravity. However, attempts to condition adults to saltier brine of 1.12 specific gravity were rarely successful and reproductive performance of the few shrimp conditioned was poor. Evidently there is an optimum brine range for Artemia. involving more fundamental biological aspects than previously reported.