Primary productivity and production measurements and their relationship to observed variations in the concentrations of nutrients (N and P), CO 2, pH, temperature, dissolved oxygen and solar radiation were studied in an 8 m deep sewage stabilization pond from October 1986 to December 1987. Two types of tests were carried out: short-term and long-term. The latter permitted the transformation of short-term measurements into daily measurements and the obtention of the relationship between the time of day and primary production. The measurement of primary production was performed using the 14C technique. The highest primary productivity values were detected during the spring-summer period, which was characterized by high temperatures and an increased degree of solar radiation. The maximum value was obtained during June (14.38 mg C mg Chl −1 day −1) and was accompanied by: (a) a decrease in the concentration of nutrients (N and P) and CO 2, (b) an increase in pH levels and dissolved oxygen concentrations and (c) a significant proliferation of cyanobacteria (which indicated a low organic loading).