The aim of the study is to establish the effect of the preparation DEODAN on leukopenia induced by chemotherapeutics in oncological patients. DEODAN is an oral preparation, obtained from lyzozyme lysates of Lactobacillus bulgaricus strain "I. Bogdanov patent strain tumoronecroticance B-51" ATCC 21815, called shortly LB51. In the study there are included two groups of patients--from National Oncological Centre, Sofia, the other from Clinic of Medicine, Bertha Academic Hospital, Clinics of Duisburg, Duisburg. All the patients, (78) have undergone combined chemotherapy. In all patients, leukopenia has been established in moderate and medium levels. The scheme of the application of DEODAN has been 3 g, three times a day before meals, from the first day of establishing the disturbances of the haemopoesis. The treatment lasted until the restoration of the haematological values. Only DEODAN was applied. The results obtained show that the recovery of the WBC count (values above 3000) took place in all of the patients between days 3 and 5. None of the patients displayed any infectious or febrile complications, as a result of the applied chemotherapy and the treatment with the preparation. DEODAN also improves the general condition of the patients.