This study was conducted to estimate the kinetic constants of benzene-acclimated biomass at optimum conditions and investigate the effectiveness of soil inoculation to expedite the biodegradation of benzene. A complete-mix, bench-scale, continuous-flow, activated-sludge reactor was used to develop organisms capable of utilizing benzene as a sole carbon and energy source. Settled pond water was used as seeding inocula and about 2000 mg/I of MLSS was maintained at the steady state with the MCRT of 7 days. The culture was used to inoculate the experimental bottle equipped with a sampling port. A series of different initial concentrations of benzene were established in the bottles for the batch growth tests. Samples were drawn every hour and the optical densities were measured at 540 nm in order to assess the growth rate. A nonlinear least-squares regression technique was employed to estimate the constants of the Haldane equation (an inhibition function). µ_m was 0.31 hr⁻¹, K₂ was 1.36 mg/I and K_i, was 1.50x10¹⁵' mg/I in the range of 14 - 491 mg/I of benzene. A small amount of the acclimated bacteria was added to the normal moist subsoil containing 100 mg/I of benzene and enough mineral nutrients. The soils were put in septum-capped glass bottles and incubated in the dark for a month. The benzene concentration in the autoclaved bottles did not decrease during the incubation period while that in the inoculated bottles was reduced to zero within 4 days and that in the uninoculated bottles was reduced to zero within 13 days. / M.S.