The effects of superficial gas velocity in the riser (U-Gr) and gas entrance velocity (v) on the growth of Haematococcus pluvialis cultivated in a split-cylinder internal-loop airlift photobioreactor were investigated. Cell growth I decreased when UGr and v were increased above 12 mm s(-1) and 22.8 m s(-1), respectively. The maximum cell density of H. pluvialis was 110 x 10(4) vegetative cells ml(-1) and the chlorophyll-a titer was 7 mg l(-1). The cell damage in the photobioreactor was greater when v was increased by an increase in UGr rather than by a decrease in sparger internal diameter. The overall volumetric mass transfer coefficient (k(L)a) of the photobioreactor was measured at the same U-Gr (6-24 min s(-1)) and v (12-80 in s(-1)). The kLa values' reached in the airlift photobioreactor were between 10 h(-1) and 32 h(-1).