Abstract.We describe the effect of inorganic mercury on the emergence, hatching and growth of Artemiafraneiscana (commercially obtained). At concentrations as low as 0.01/tmol 1-1, mercury delays development of the organism, but the effect on the final number of developed brine shrimp is small. At higher concentrations, mercury has a dramatic effect, inhibiting the developmental process at the emergence and hatching stages. As recorded by light and scanning electron microscopy, organisms stalled at emergence are not immediately killed. Their eye spots continue to darken and some may hatch although partially enclosed in the cyst shell. Completely emerged prenauplii in the presence of mercury often have an abnormal oval shape while hatched organisms may display shortened and deformed bodies and exhibit restricted movement. The results demonstrate that emerging A. franciscana are very sensitive to inorganic mercury and the potential usefulness of this organism for the study of metal effects upon physiological processes is indicated.