The study of primary production from phytoplankton in estuarine regions is of basic importance, to projects of culture of oysters, shrimps and fishes. In this paper a study was made of the primary production in the Rio Curú's estuary (Ceará-Brasil), during the period from September, 1977 to May, 1978. We used the Winkler's method to make the measurement of productions. The data obtained on oxygen produced varied from 0.03 to 0.04 m LO2 |l| hour of light, for net production and 0.01 to 0.04 ml O2 |l| hour of light for the total production. Qualitative and quantitative studies were also made to obtain the dominant species and the most abundant and most frequent species.
