The cultivation of photosynthetic microorganisms such as the microalga Spirulina platensis can provide an alternative source of food. The water in Mangueira Lagoon (Rio Grande do Sul state, southern Brazil) has several required nutrients for the growth of Spirulina and could be added to culture medium to reduce the cost of producing S. platensis. Although little studied, repeated batch cultivation is a very useful technique because it has a better cost–benefit ratio than other cultivation methods. In a series of runs, we studied the influence of cell concentration, renewal rate and strain on the specific growth rate and biomass productivity of S. platensis during repeated batch cultivation, the runs taking place in 2-l Erlenmeyer flasks for 2160 h at 30 °C and a light intensity of 2500 lux under a 12 h photoperiod. The three factors studied had a significant (P<0.05) effect on the results (specific growth rate and productivity). Using Zarrouk's medium, the highest specific growth rate (μX) was 0.111 day−1 while the biomass productivity (PX) was 0.0423 g l−1 day−1, while Mangueira Lagoon water supplemented with 10% Zarrouk's medium gave μX = 0.113 day−1 and a productivity PX=0.0467 g l−1 day−1. These values were two to three times higher than the results obtained in batch cultivation, indicating that the repeated batch cultivation of S. platensis is attractive and convenient.