Arthrospira (Spirulina) platensis was cultivated in bench-scale open ponds on a modified Schlosser medium. The fed-batch exponential supply of ammonium sulfate at defined feeding time and pH allowed obtaining optimum results in terms of biomass growth and composition. The cultivation conditions established herein will constitute the main starting point of a wider study in which this cyanobacterium is employed for fixation of CO2 from industrial plants. The industrial exploitation of these results appears to be promising also for single-cell protein production.