The paper deals with possibilities and prospects of application of reliability theory in biology and particularly in gerontology. The possibilities and limitations of existing reliability methods are analyzed with respect to their eventual use in biology, and new methods suitable for analysis of changes in the reliability of biological systems during their aging process are searched for. A new method is proposed for reliability parameter estimation of elements and subsystems forming biological systems. Application of the method could bring new information regarding the causes of declining reliability of biological systems during their aging. Application of the method is demonstrated by an analysis of reliability of the human organism, and the results are compared with some current theories of aging.