The growth kinetics of 6 species of marine heterotrophic nanoflagellates (5 to 13 mum) were compared. The maximum specific growth rates (mu(max)) of the flagellates ranged from 0.035 to 0.21 h-1 and the half-saturation constants (K(s)) ranged from 1.1 to 45 x 10(6) bacterial cells ml-1. Theoretical threshold concentrations were calculated for each flagellate and the values of these generally ranged from 2 to 10 x 10(4) bacterial cells ml-1. The flagellate yield values (Y), maximum uptake rates (U(max)) and maximum clearance rates (F(max)) for each flagellate species ranged from 0.3 to 13.2 x 10(-3) cells bacterium-1, 5 to 259 bacteria cell-1 h-1 and 1 to 58 nl cell-1 h-1 respectively while volume-specific clearance values ranged from 1.4 x 10(4) to 8.7 x 10(5) body volumes h-1.