Production of acetic acid from ethanol byAcetobacter aceti attached to a variety of support materials has been examined in fixed-film packed bed fermenters. Overall batch acid productivities with triangular ceramic particles and nylon mesh were respectively 56% and 30% greater than that for woodshavings, with comparable high acid yields. The highest batch acid productivity attained was 0.75 g/l h with the ceramic support. Continuous operation with the same material resulted in an acid productivity of 4.0 to 4.5 g/l h at a yield of 80%. This was increased to 10.7 g/l h by feeding oxygen-enriched air to the fermenter.