The toluene-degrading bacterium Acinetobacter sp. Tol 5 is highly adhesive to solid surfaces owing to two filamentous cell appendages, namely, anchors and peritrichate fibrils. When growing this bacterium in the presence of a carrier made of polyurethane foam, almost all the cells adhered to the surface of the carrier. In contrast, when Tol 5 cells were grown in the absence of the polyurethane carrier, the cells were suspended as aggregated cells or individually dispersed cells. The aggregated cells possessed the cell appendages and showed an adhesiveness similar to that of cells grown in the presence of the carrier, while the dispersed cells scarcely produced the cell appendages and showed a low level of adhesiveness. The dispersed cells started to adhere to the polyurethane carrier by producing the filamentous appendages within 30 min of the addition of the carrier as a substratum and toluene as a carbon source. Peritrichate fibrils just sprouting and growing anchors longer than 3 pm were observed when the cells started to adhere. This suggests that the presence of surface areas sufficient for adhesion might trigger cell appendage formation in Tol 5 cells for adhesion by increasing the amount of cell contact with the surfaces.