Gracilaria is one of the main commercial seaweeds exploited along the Chilean coast. In 1983, 10.6 x 105 tonnes of this alga were exported as raw material, returning a revenue of 7 x 106 dollars (Servicio Nacional de Pesca, 1983). Gracilaria has been planted on sandy bottoms in protected bays with normally calm water using uncomplicated methods. The plantations have been affected by storms and currents which cut portions of the thalli or completely bury the plants in the sand (Santelices et al., 1984). Ocean currents may deposit the seaweeds on beaches distant from their original locations. The steepness of shores and unpredictability of water movements affect most of the highly productive Chilean coast, restricting possible seaweed cultivation to only a few bays. An alternative method of culture for this alga which avoids natural stresses involves open-circuit outdoor tanks. We now report on 14 months of experience in culture of Gracilaria in tanks where light and the flow of water and air were controlled, and where productivity of Gracilaria was routinely measured under varied conditions.