Bromoperoxidase is an enzyme found in marine macroalgae that catalyzes the bromination of organic substrates. Photosynthetic microplantlet suspension cultures derived from the macrophytic red alga Ochtodes secundiramea were shown to possess bromoperoxidase. The optimum pH for O. secundiramea bromoperoxidase activity in cell-free extracts was 6.0, and the half-saturation constant for bromination of the exogeneous substrate monochlorodimedone (MCD) was 18 muM. O. secundiramea microplantlets were cultivated in a bubble-column photobioreactor at an incident light intensity of 38 muE m(-2) s(-1) (71% of light-saturated photosynthesis, 10:14 light:dark photoperiod), and the kinetics of cell growth and bromoperoxidase production were followed. At these conditions, the specific growth rate was 0.052 day(-1). The lowest specific bromoperoxidase activity of 0.3 mu mol MCD g(-1) cell min(-1) occurred during the midexponential phase of growth, and then increased steeply to 1.9 mu mol MCD g(-1) cell min(-1) during the late stationary phase, suggesting that bromoperoxidase production was part of secondary metabolism. The estimated bromoperoxidase content in the cell mass at late stationary phase was 67 mug g(-1) dry cell mass, demonstrating that bioreactor production of marine bromoperoxidase is feasible.