A review with 51 refs. on the mechanisms of microbial deterioration of materials in papermaking is presented. Generally, all kinds of microorganisms, i.e., algae, bacteria and cyanobacteria, fungi, and lichens, are able to attack and degrade materials. The deterioration is caused by the excretion of metabolic intermediates and(or) end-products, as well as exo-enzymes. Depending on the use of a material, a discoloring of a resin or a total destruction of a material, this attack may result in a serious microbiol. influenced corrosion damage. Although many microorganisms are known to participate in these processes, the mechanisms of action may be summarized by 8 main categories; usually, the deterioration of a material is caused by a combined action of factors. However, chem. methods often fail to detect the mechanisms properly because some compds. may be subject to a metabolic turnover (org. acids, N compds. etc.). Microbiol. analyses are necessary for clearing up the mechanism of attack.