When viewing the hygienic aspects from composting plants, one has to consider not only the hygienic aspects of the product, but also the airborne hygienic aspects. This is very important regarding the microbial air pollution and possible occupational health hazards. Compared to the results of other tests performed in hospitals and offices, the composition of the air in the composting plant is heterogeneous, both in quality and quantity. Thus, special attention is needed concerning the air-particle sampling methods and the microbial investigation parameters. Our own research was done using measuring methods, which considered the complex air composition as well as the high concentration levels. The samples were extracted by the six-stage Andersen sampler. This method ensures that even extremely sensitive bacteria or moulds will survive, provided that the one-minute sampling time is respected. In addition to this, it is possible to measure microorganisms in various sizes. It was decided to take the samples only for the duration of one minute. This was done to reduce any technical incorrections and also to provide representative results. The amount of the one-minute samples was set at 30 single samples. This is based upon the German technical regulation named TRGS 402. Here the relationship between the number of samples taken and the length of sampling time is laid down when measuring hazardous substances. In all cases, three samples were simultaneously collected. Total mould and total bacterial counts covering the maximal occurring concentrations were determined. The obtained results show that in a short period of time and depending upon the heterogeneity of the input, both the bacteria and mould concentrations vary. It has been observed that an extremely high air pollution level was reached during shredding and transpositing. Through the use of statistical methods, one is able to estimate the relevance of microbial air pollution. Measuring techniques and strategies have to be adapted to the current research parameters and environmental conditions. Very large concentration differences were shown within a short period of time. Therefore measuring strategies must be able to consider this. In order to detect the average occupational hazard and in order to be able to get reproducible results, many random tests have to be taken. Resulting from the statistical comparisons, between the background concentrations and the moccupational concentrations, one is able to win an objective evaluation