Demographic responses of the estuarine copepod Eurytemora herdmani to several combinations of temperature and salinity were evaluated in the laboratory. Observed values of the intrinsic rate of population increase, r, ranged from -0.069/d to 0.088/d. Over the experimental range of 15 to 35 0/00 and 10 to 20 C, the observed values of r at 20 to 30 0/00 were higher than those at 15 or 35 0/00; observed values of r at 20 C were lower than those observed at the lower temperatures. Temperature was found to influence the rate of population growth primarily through age of reproduction while salinity effects were primarily through fecundity.