Frailty, as a geriatric syndrome, is characterised by the increased vulnerability of the elderly person to internal and especially exter-nal stressors. The aim of laboratory diagnostics in the context of the concept of frailty is to record the conditions which encourage the development of frailty, in order to improve these conditions through individual measures or to avoid them for the purpose of preventing frailty. After a presentation of the features of labora-tory diagnostics in old age, this article examines haematological aspects, the importance of an adequate vitamin supply, particu-larly of vitamin D and the adequate description of endocrine func-tions.