Effects of the insect growth regulating compound, Dimilin [1-(4-chlorophenyl)-3-(2,6,-difluorobenzoyl)-urea], on reproduction in brine shrimp,Artemia salina, were investigated using pair mating experiments. Reproductive performance was compared for 5 groups of 15 mated pairs each, exposed to one of 5 test solutions (1, 2, 5, 10 ppb Dimilin and a control). Significant reduction in reproductive lifespan was evident in adults exposed to 2, 5, and 10 ppb; in addition, males consistently outlived females in all Dimilin exposures. Survivorship of nauplii produced viviparously by mated pairs was comparable to controls, except in the 10 ppb exposed group. Cysts, produced oviparously by treated pairs at all Dimilin concentrations, displayed significantly lower mean hatchability (<4.8%) than controls (22.6%) upon rehydration. Newly hatched nauplii (24 h old) were exposed to concentrations of Dimilin (10,000 ppb, 1000 ppb, 100 ppb, 10 ppb, 1 ppb and a control) for a l2-day period. Nauplii exposed to concentrations greater than 10 ppb died within 3 days or less, while survival of nauplii exposed to 10 ppb and 1 ppb was comparable to controls.