Respiration rates and $Q_{10}\text{'}{\rm s}$ of 1-day-old brine shrimp nauplii were affected significantly by radiation, the salinity of the water, and the interaction between the two factors. Respiration rates were measured in salinities from 5 to 200%. Irradiated nauplii received doses of 60 Co radiation of 10,000 to 80,000 rads. In general, respiration rates of irradiated nauplii were significantly lower than those of unirradiated nauplii at salinities of 5, 50, and 200%, but were higher at 100 and 150%. When nauplii were in the highest salinity, 200%, each increase in radiation above 10,000 rads caused a corresponding decrease in the rate of respiration. Similarly, at each salinity the nauplii exposed to the highest radiation dose, 80,000 rads, had the lowest rate of respiration. The highest levels of radiation and salinity acted synergistically and depressed the respiration rate to the lowest point. The greatest effect on $Q_{10}\text{'}{\rm s}$ was at the highest salinity. At this salinity, Q 10 values for all irradiated nauplii were significantly lower than for controls or for irradiated nauplii at other salinities.