This technical protocol describes a laboratory test method to evaluate the transformation of chemicals in liquid bovine and pig manures under anaerobic conditions and is primarily designed for veterinary medicinal products (VMP) and biocides. The environmentally relevant entry routes into liquid manures occur via urine and feces of cattle and pigs in stable housings after excretion of VMP (as parent compounds or metabolites) and after the application of biocides in animal housings (e.g., as disinfectants or insecticides). In loose housing stables with slatted floors, the excrements are discharged into manure aboveground silos or underground pits. After the storage of liquid manures up to several months, they are applied to farmland and grassland soils as organic fertilizers. Via this route, VMP and biocides may enter soil environments. Thus, the persistence of the chemicals during manure storage under anaerobic conditions decides on the environmental relevance of this entry route.