Batch experiments were performed for the aerobic co-metabolism of 1,1-dichloroethylene (1,1-DCE) by Achromobacter sp., identified by gene sequencing of 16S rRNA and grown on benzene. Kinetic models were employed to simulate the co-metabolic degradation of 1,1-DCE, and relevant parameters were obtained by non-linear least squares regression. Benzene at 90 mg L-1 non-competitively inhibited degradation of 1,1-DCE (from 125 to 1,200 mu g L-1). The maximum specific utilization (k(c)) rate and the half-saturation constant (K-c) for 1,1-DCE were 54 +/- A 0.85 mu g h(-1) and 220 +/- A 6.8 mu g L-1, respectively; the k(b) and K-b for benzene were 13 +/- A 0.18 mg h(-1) and 28 +/- A 0.42 mg L-1, respectively. This study provides a theoretical basis to predict the natural attenuation when benzene and 1,1-DCE occur as co-contaminants.