A semidifferentiated tissue culture consisting of linear filaments in liquid suspension was established from Acrosiphonia coalita, a cold-water green macroalga known to express pharmacologically active oxylipins deriving from lipoxygenase matabolism of linolenic acid. The tissue was vegatively propagated by blending the filaments down to 1 to 5 mm in length prior to subculture. The filamentous A, coalita tissue suspension was successfully cultivated in an illuminated, 3-L stirred-tank bioreactor at 12 degrees C, 0.46-vvm aeration rate, 250-rpm mixing speed, and incident illumination intensity of 77 mu E m(-2) S-1. The mean specific growth rate over the exponential phase was 0.185 day(-1) and a final cell density of 1083 mg dry cell weight (DCW) L(-1) was achieved within 15 days of cultivation from an initial cell density of 200 mg DCW L(-1). The addition of 3500 ppm CO2 to the aeration gas provided a maximum CO2 transfer rate of six times the maximum CO2 consumption rate and stabilized the pH to 8.0 during the light phase of growth, but did not improve biomass productivity.