The soil-born pathogens Thielaviopsis basicola (Berk. u. Broome) Ferraris and Ceratocystis paradoxa (Dade) C. Moreau cause black root rot on many crops, that leads to extensive qualitative and quantitative losses in yield and storage. The crop rotation plays a decisive role at the pest management. The inoculum level in the soil describes a contributing factor for the planning of the crop rotation. In this study bioassays were validated, which determine the inoculum level on the basis of the symptom development. In addition a test system was developed, which uses the development of endoconidia as a quantitative scale for soil infestation. A bioassay of BIDDLE (1984), in which peas were seeded in soil samples, was validated in greenhouse tests. Other authors described Bioassays with carrots as baits, which were exposed to the soil-samples. As carrots are host plants of the pathogens, the test material shouldnt be bought at a food retailing, but has to be raised under pathogen-free conditions. At the date of carrot sowing the quantity of arrival samples is unknown. Therefore growing carrots in pathogen-free conditions is a big effort for incalculable material requirements. Experiments, to eliminate a pre-infestation of the carrots due to the use of the carrot cores (surface disinfected), failed. The pathogens invade the cores before symptoms develops. Therefore other materials free from pathogens were tested as baits, for example zucchini fruits. Because of the pathogens weak competitiveness no alternative bait material could be found. Of the validated bioassays the pea-test of BIDDLE (1984) performed the best, despite the long test duration of five weeks. By means of the test results prognoses can be made, concerning the disease risk for peas and beans due to Thielaviopsis basicola, when growing on the tested field. Further experiments concerning the disease risk for other crops and due to Ceratocystis paradoxa and corresponding yield losses are required.